Prickly Pear Cacti in Hawaii? Ouch!

I spent most of my career as an earth scientist in the deserts of the American West, where there are tree-sized cactus species everywhere. So it’s natural that I came to think of “big cacti” as growing ONLY in places like the arid sand deserts of mainland North America. Imagine my surprise and confusion when I encountered hundreds of thickets of a really large species of cactus, the Prickly Pear, on Maui, a tropical island in the middle of the Pacific Ocean that receives more than 300 inches (760 centimeters) of annual rainfall.

Mature Prickly Pear Cactus growing on cliff face near Ho’okipa Beach, east Maui.
[ Click on image to view larger version. ]

The Prickly Pear Cactus, Opuntia ficus-indica (“Panini” in Hawaiian*) was introduced (ostensibly as cattle fodder) to the Hawaiian Islands early in the nineteenth century but is now naturalized on all the main islands. It prefers sunny open land on gentle slopes, although it is not unusual to see large mature plants clinging to nearly vertical cliff faces, particularly in drier leeward coastal areas. It prefers rocky well-drained soils with a pH range of 7 to 8.5, soil conditions that increase root growth and branching in this species of Opuntia. It also tolerates moderately saline soils and air temperatures ranging from minus-6º C to a high of 65º C.

A very mature tree-like Prickly Pear Cactus growing in a cattle pasture on Pulehu Road, south Maui. Measured more than 10 meters horizontally!
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The Prickly Pear is a massive trunk-forming segmented cactus that typically reaches heights of 3 to 5 meters with a lateral span of two to three times its height at maturity (usually at 20 years of age). The individual leaves (“pads” or “nopales”) of this species are edible, but are covered with widely spaced aureoles that include one to as many as six white or yellowish spines 1-3 cm long. In addition to these formidable spines, aureoles include numerous glochids, tiny hair-like spines that are smaller than typical spines but no less formidable. Incautious handling of pads and fruit of the Prickly Pear can cause scores of these tiny spines to lodge in the skin and soft tissues of the handler where they can remain for days or weeks, often becoming infected. Old pads form the substantial woody stem of the tree.

A very mature tree-like Prickly Pear Cactus growing in a cattle pasture on Pulehu Road, south Maui. Measured more than 10 meters horizontally!
[ Click on image to view a larger version. ]

The fruit (“tunas” or “pears”) of this species is typically greenish white to yellow, yellowish brown, or reddish-purple (depending on the strain). Individual fruits are fleshy and barrel-shaped, and at maturity are about 10 cm long and half that wide. Like the pads, the tasty nopales possess glochids in their aureoles and must be carefully handled and properly prepared prior to consumption.

A “nopale” (leaf) with several fruits (“tunas”) of a Prickly Pear Cactus growing in a cattle pasture on Pulehu Road, south Maui.
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The flowers of the Prickly Pear are pollinated by insects. They are cup-shaped, bright yellow or orange, and 5-7 cm in diameter. They form on the perimeters of individual pads and bloom in spring or early summer.

Flower of a Prickly Pear Cactus, Pulehu Road, south Maui.
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Seeds are dispersed by birds, feral pigs, and lizards that feed on the fruits. The seeds from intact fruits and animal droppings germinate after long rainy spells followed by months of hot weather. However, seeds in the soil can remain viable for several years. Vegetative reproduction is accomplished by cladodes (flattened succulent segments and stems) falling close to parental plants and quickly taking root. The latter form of reproduction often results in dense stands of many large plants.

Healthy nopale of a Prickly Pear Cactus, Pulehu Road, south Maui.
[ Click on image to view a larger version. ]

Opuntia ficus-indica was probably introduced into Hawaii from Mexico by Don Francisco de Paulo Marin in about 1809. Originally intended to serve as a barrier in cattle pastures (panini means “fence wall” in Hawaiian*), cattle fodder, and a human food source, its innate shortcomings prevented it from becoming popular with ranchers. Cultivated in the wrong place, this species can develop into a destructive weed: it can overrun cattle grazing lands, eventually ruining them with its invasive overgrowth. It also may out-compete certain native plants and upset local ecosystems. By 1910, several thousand acres of pastureland were under cultivation with Prickly Pear Cactus. Although only the spineless varieties were initially established, the species gradually reverted back to the spiny wild genotype by means of genetic recombination and selective grazing pressure. Over a period of nearly 200 years, there were serious invasions of Prickly Pear in many countries (including the Hawaiian Islands).

New bud growing on the tip of a “nopale” of a Prickly Pear Cactus.
[ Click on image to view a larger version. ]

Biological Control — At one time, Prickly Pear Cactus nearly overran Maui and the neighbor islands. The plant is considered a pest species due to its ability to spread rapidly beyond the areas in which it was originally cultivated. The environmental threat posed by invasions of the cactus became so grave that large-scale biological control programs had to be initiated. It was discovered that the most effective biological control agent was the tunneling larval caterpillar of the Cactus Moth (Cactoblastis cactorum), a species native to Argentina. Releases of the caterpillar in Australia (where Opuntia ficus-indica infestations most seriously affected the environment) in the early twentieth century led to almost complete control of the species. On the strength of the successes in Australia, Cactoblastis was introduced into Hawaii in 1950.

A larval caterpillar of the Cactus Moth (Cactoblastis cactorum) thinking about its next meal. Kula, south Maui.
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The larvae of Cactoblastis cactorum feed on the entire cactus plant, burrowing into the fruits, pads, stems, and root system where they live communally, devouring the entire biomass from the inside out, leaving nothing above ground. Even if the cactus plant is only subjected to limited predation by the caterpillar, the resulting tissue damage facilitates the growth of bacteria and fungi, hastening the destruction of the plant. The Cactus Moth larvae are capable of destroying entire stands of cacti. In 1985 they were introduced into an invasive stand of Prickly Pear Cactus in Volcano National Park on the island of Hawai’i, successfully eliminating the threat of a damaging invasion. Today there are many isolated stands of Opuntia ficus-indica in the upland mesic forests of the western slopes of Maui’s Haleakala volcano, especially in the areas surrounding the towns of Pukalani, Makawao, Kula, and Ulupalakua. The cacti are relatively abundant here, but most individuals are in poor condition due to predation by the moth larvae.

Medicinal and Pharmacological Uses — Despite its well-deserved reputation as a noxious weed and invasive species, the Prickly Pear Cactus does possess some redeeming characteristics: recent laboratory studies have shown that extracts of various parts of the plant have significant medicinal benefits and are potential sources of raw material for the pharmaceuticals industry.

Prickly Pear fruit possesses antioxidants – When a cell’s capacity to protect itself fails, oxidative stress occurs. Oxidative stress results from an oxidant/antioxidant imbalance, an excess of oxidants, and/or a depletion of antioxidants. A considerable body of recent evidence suggests that oxidative stress plays a major role in several aspects of acute and chronic cellular and tissue inflammation. U.S. Department of Agriculture studies have shown that fruits like blueberries, cranberries, raspberries, strawberries, apples, and the Prickly Pear contain high concentrations of inflammation-fighting antioxidants. Researchers reported that betalains (a class of red and yellow indole-derived pigments found in plants like the common beet) contribute to the free radical-scavenging and antioxidant activities of Prickly Pear fruits. The Prickly Pear Cactus is the only plant species that contains all 24 of the known betalains, which are also a class of rare and potent healing antioxidants. These antioxidants are used to treat many serious inflammatory diseases in humans. They may also prove useful in promoting healing of organs and tissues, as well as mitigating the more unpleasant symptoms accompanying an alcoholic hangover. Not bad for a noxious weed, eh?

A Postscript for DIYers
If you plan to try your hand at preparing Prickly Pear tunas and nopales for your dinner table, be sure to first visit the website “How to Eat Prickly Pear Cactus”. It contains very detailed instructions for removing the nasty spines and double-nasty glochids. Please, BE CAREFUL if you eat fruits you’ve prepared yourself! My advice: try them at a genuine Mexican restaurant where they know how to prepare these bad boys!

Malama pono!

Kiawe (Prosopis pallida): Hawaii’s Tropical Mesquite

A couple of years ago I was photographing some volunteers at a Beach Cleanup Day at Kanaha Beach park near Kahului on Maui’s windward side. Part of the cleanup involved piling up some large tree branches that had been cut the day before by a Maui County tree-trimming crew. As I and the volunteers began stacking the cut limbs by the side of the access road for the County people to dispose of, a pickup truck full of locals hurriedly pulled up behind us. The driver asked if he and his boys could have all of the cuttings. The crew leader agreed as long as they took the entire pile with them. “No problem, bruddah! Dat’s Kiawe and it’s great for makin’ barbecue fire!” In an instant, the slash pile was thrown into the bed of the truck by its enthusiastic passengers. The truck then sped off down the dirt road, its occupants all waving happily as if it was double-pay day. In this way I was introduced to the Kiawe, Maui’s tropical mesquite tree.

A healthy mature Kiawe tree helping to stabilize the berm on Kealia Beach, Ma’alaea Bay, Maui.
(To view a larger version, click on image.)

Prosopis pallida is a perennial that belongs to the Mimosoideae subfamily (mesquite & mimosa) of the Leguminosae/Fabaceae family. It is commonly referred to by its Hawaiian name “kiawe” (pronounced “kee-AH-vay”). As with all other members of this family, it produces its seeds in pods referred to as “legumes”, hence the common name for the family.

The outer bark and foliage of the Kiawe tree.
(To view a larger version, click on the image.)

Physical Characteristics — Under ideal conditions, Kiawe trees can grow to be more than 30 m tall and form dense, continuous forest canopies (one of the few species of dry coastal trees to do so). However, they may also develop into gnarled, stunted bush-like trees in dry, wind-swept areas with poor soil such as those found in stabilized sand dunes and beach berms.

Leaves emerge from a common node on the twig, which changes direction often as it grows, giving it a corkscrew or zig-zag appearance when mature. The small, delicate-looking leaves (usually less than 2 cm long by a half a centimeter wide) are doubly compound with 3 to 4 pairs of stemlets branching from the main leaf stem. The twigs and branches include a fair number of very formidable thorns (see image below) notorious for drawing blood from careless beach-goers who seek out the Kiawe’s ample shade.

In the spring, small yellowish-green flowers are borne on long (8 to 15 cm) cylindrical spikes that give way to dense clusters of long (10 to 20 cm) yellowish-brown seed pods. The 10 to 20 seeds per pod (see image below) are encased in a sticky, sugary pulp.  The heartwood is dense-grained and hard, making it a favorite fuel for cooking fires on Maui and throughout the world. Generally, the root system is shallow, spreading out laterally; but in arid soils it easily develops a long taproot.

A typical Kiawe twig displaying its characteristically delicate foliage and very nasty thorns.

Kiawe seed pods fall from a single tree’s branches by the thousands, ensuring that many seeds survive & germinate.
(To view a larger version, click on the image.)

Introduction to Hawaii — Prosopis pallida is native to the arid coast of northwestern South America. In 1828 it was introduced to the Hawaiian Islands by Father Alexis Bachelot, the head of the first catholic mission to Hawaii. He planted a tree on the grounds of the Catholic Mission on Fort Street in Honolulu that he had raised from the seed of a Peruvian tree growing in the royal gardens of Paris. By 1840, the progeny of that single tree became the principal shade trees of Honolulu and were already spreading to the dry leeward plains on all of the neighbor islands, including Maui.

Growth Habits — A Kiawe seedling’s survival depends on receiving sufficient rainfall and sunlight (the seedlings do not tolerate constant shade) during the first few weeks after germination. The seedling can grow more than one meter in its first year under the right conditions. It will produce a strong and rapidly growing taproot system that can penetrate deep into even the hardest soils. Many old trees have been saved as garden and park trees during land development and have grown to large sizes with constant irrigation. Trees that grow on coastal plains where groundwater is shallow and abundant grow to be quite large, but they develop shallow root systems and windstorms can topple them easily. Once mature, growth is very slow compared to that of other trees under similar conditions. On windy or dry sites, Kiawe grows as a shrub or a small twisted tree only a few meters tall. Where it grows in strong trade winds, it is sculpted and shaped by the prevailing winds and lies along the slopes as a rounded bush. Although it is a coastal species, Kiawe is easily defoliated by the windblown salt spray of winter storms. Kiawe trees grows in areas where fire hazard is often extreme. Trees rarely survive slow-burning fires; they are usually killed outright by fire.

Invasive Habits — Once Kiawe was introduced to Hawaii it quickly became a pest species, invading, out-competing, and overwhelming native grass species and woody plants. It is a successful invasive species due to its ability to reproduce in two ways: production of large numbers of easily-dispersed seeds, and vegetative growth (by suckering) to create thick monotypic stands that shade out all other nearby plant species. It requires less than four inches of annual rainfall to establish itself and survive. It survives well in dry environments due to its extremely long taproot. It is so efficient at withdrawing moisture from soil that it can kill nearby plants by depriving them of water. It is often found growing in areas where other plants do not grow, such as sandy, dry, degraded slopes; salty soils; disturbed areas; and rocky cliffs.

A dense, continuous canopy of Kiawe trees growing along a beach front in the Kawalilipoa neighborhood of Kihei, south Maui.
(To view a larger version, click on image.)

Ironically, it is these very traits that have made Prosopis species so valuable in efforts to control soil erosion due to desertification in Africa and South Asia. Kiawe serves a similar purpose on islands such as Maui where beach erosion is a serious problem.

These well-established Kiawe trees rooted in the unstable sands of Kealia Beach protect a delicate intertidal marine habitat from the ravages of wind-blown sand and storm-driven waves.
(To view a larger version, click on the image.)

Maui’s Blue Morning Glory: Ipomoea indica

Before I moved here I never gave the Morning Glory a second thought: to me it was just a colorful but mostly innocuous ground cover on the beaches of California where I grew up. However, on a small island like Maui they are kind hard to ignore because there are so many of them and they are seemingly everywhere you look. From the high-tide line on most of our white-sand beaches to almost 4,000 feet up Haleakala’s volcanic slopes, their cookie-cutter-perfect flowers and massive amounts of foliage and choking vines spill out over the landscape, engulfing everything from derelict automobiles to the headstones in cemeteries.

Flowers & foliage, the Blue Morning Glory, Ipomoea indica.
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The Morning Glories are plentiful in the Hawaiian Islands for two reasons: (1) they are able to adapt to almost any environment and (2) they propagate like oversexed rabbits. Their roots can absorb large quantities of seawater, they tolerate almost any kind of soil, and though they may be torn to shreds and small pieces they are still capable of taking root and flourishing. They choke off the saplings of competing species and shade-out established trees and bushes. On the other hand, Morning Glories can be important pioneer species that stabilize sand dunes and prevent beach erosion.

A solitary blossom of Ipomoea indica.
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The Blue Morning Glory (Ipomoea indica)

Ipomoea indica is a perennial vine native (indigenous) to Hawaii (“koali awa” in Hawaiian). It is variously known as Ocean Blue Morning Glory, Blue Morning Glory, and Blue Dawn Flower. It’s also called a “Dunny Creeper” in Australia (a “dunny” is an outhouse toilet), referring to its habit of covering everything in sight with its vines, including small out-buildings. Its geographic origin is uncertain: it may be native to the West Indies. It is now naturalized throughout the tropics and is found on all the main Hawaiian Islands. It is usually found at lower elevations (below 200 m) but has been known to grow at altitudes above 1,200 m.

Close-up of a mature Ipomoea indica plant. Note the characteristic 3-lobed leaves.
(Click on the image to see a larger version.)

Ipomoea indica prefers sunny open ground in a moist environment, but will tolerate seasonal dry spells once it is well established. It is a perennial that grows as a sprawling (ground-hugging) vine that produces a dense ground cover, but it is often seen climbing and twining over other plants. The vine itself (called a “stem”) is softly hairy and may grow to more than seven meters in length. The distinctively shaped leaves are large (as much as 15 cm wide and 17 cm long) and numerous. They may be heart-shaped when immature; mature leaves are 3-lobed to 5-lobed with pointed tips. The upper and lower surfaces of the leaf are covered by silky, short, closely-spaced hairs.

The flower is large (as much as 80 mm in diameter) It usually ranges in color from sky blue to purple-blue; less commonly it may also be light magenta and reddish-pink. It has paler mid-petal bands and a pink to whitish tube inside. The petals (3 to 15 per flower) are joined, which accounts for the distinctive trumpet-like shape of the flower. Ipomoea indica sets flowers all year, continuously flowering during warmer months. The short-lived flowers are replaced as they fall from the vine.

The fruit is a small (about 10 mm in diameter) 3-chambered spherical capsule. These are rarely produced by the plant. It has almost no self-fertilization and so grows vegetatively: its preferred method of propagation is by the production of numerous stolons, stems that grow above ground and are able to produce both roots and foliage. Individual stolons are readily detached from the parent plant and dispersed by mechanical means such as flooding, stream flow, landslides, or human activity (ground clearing and weed removal). Even when badly damaged, a plant can easily recover 4-6 m of its length in a single growth season. One theory about why Ipomoea indica evolved this unique reproductive behavior is that the species is a sterile hybrid and its genes are self-incompatible.

This species contains toxic alkaloids (including Ergonovine, which bears a strong molecular resemblance to Lysergic Acid Diethylamide, or LSD) that discourage ingestion by grazing animals. This defense mechanism contributes to its prevalence as a weed species.

Photo shows the tendency of the Blue Morning Glory to choke off sunlight from other plants by spreading its tendrils and vines in all directions, wrapping itself around anything from tree trunks to derelict automobiles.
(Click on image to see larger version.)

The Blue Morning Glory is a vigorous climbing vine that not only forms a dense ground cover but can easily extend itself high into the forest canopy. The twining stems can quickly choke off the growth of seedlings of other species and smother even older well-established plants. It also poses a significant shading hazard to other species.

Hawaiian Ginger: Not just for eating

I live on a part of the Island of Maui’s leeward shore that is surrounded by and engulfed in many small private and larger public gardens and parks. The enclosed courtyard of my own housing compound is a modest botanical garden that includes tall Coconut Palms, Strangler Figs, banana trees, and many of the flowering bushes and shrubs that grow on Maui. Despite competition from the usual hordes of gaudy hibiscus and orchid tree blossoms, the plants whose flowers stand alone in that crowd of colorful blossoms and foliage are the different species of the Zingiberaceae Family, or ginger.

Now that I’ve been photographing and blogging about Hawaii’s plant life, I’ve grown to appreciate the members of this plant family because of the great variety of their size, form, and color. It should be no surprise, then, that along with all of the photographs of palm trees and hibiscus, the online photo galleries of recent visitors to our islands are crowded with images of Hawaii’s photogenic ginger species.

Pink variety of Red Ginger (Alpinia purpurata). Flower head is about 20 cm long. Hana, east Maui.
(Click on image to see larger version.)

The English word “ginger” comes to us from the French word “gingimbre” by way of the ancient south Asian words “inji ver” (literally, “the root of Inji” in Dravidian) and “singivera” (Pali), from which the Greek word “zingiberis” and the medieval Latin word “gingiber” probably were derived. As you might expect, the Hawaiian names for individual species of ginger evolved along a different linguistic line.

Aside from being the ideal subjects for amateur photographers (unlike birds and whales, they tend not to move around much), the various species of ginger have long been known for their aromatic properties and as an ingredient in prepared ethnic foods. More recently, many “root ginger” species that belong to the taxonomic family Zingiberaceae have been found to possess chemical compounds sought after by the pharmaceutical industry. Zingerone, gingerols, and shogaols are the volatile oils (about three percent by weight) responsible for ginger’s fragrance, distinctive taste, and numerous beneficial medicinal properties.

Several extracts and distillations of ginger plants possess antibacterial, analgesic, sedative, and antipyretic (fever-reducing) medicinal properties. In addition, several species of ginger are currently being researched as candidates for the treatment and cure of skin and ovarian cancer. There is also on-going research into the blood-thinning and cholesterol-reducing properties of ginger. Powdered ginger root capsules have been shown to be effective in treating and preventing the nausea associated with morning sickness and motion sickness; however, clinical studies in this area have proven inconclusive.

The following are my photographs of a few of the most common species of ginger plants growing in Maui’s gardens and rain forests. These species also grow in the garden of my own housing compound in Kihei (leeward Maui).

Close-up of the flower head of a Torch Ginger (Etlingera elatior), Hana, east Maui.(Click on image to see larger version.) 

Torch Ginger (Etlingera elatior), Hawaiian = ‘awapuhi ko‘oko‘o – A herbaceous perennial, individual plants grow in large clumps whose stalks can be as much as 6 m high with leaves as long as 85 cm. Although it is cultivated throughout the tropics and has escaped to become naturalized in some localities, its original native range is thought to be a few isolated islands in Indonesia.  Typically it prefers a moist climate with somewhat acidic soil (pH = 5.6 to 7.5). It prefers full sun but does well in the partial shade of the rain forest. It is found at altitudes up to 9,000 feet. The various plant tissues and parts of this species of ginger are rich in volatile aromatic compounds. The majority of the essential oils extracted from the leaves, stems, flowers, and rhizomes of Torch Ginger are monoterpene hydrocarbons. Terpenes are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used widely as natural flavor additives for food, as fragrances in perfume, and in traditional and alternative medicines. Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives. Vitamin A is an example of a terpene. Currently, this and other species of ginger are the subjects of extensive research into the various antioxidant compounds present in their leaves and rhizomes.

Crepe Ginger (Costus speciosus), Keanae Peninsula. The fluted “petal” is actually the male part of the flower. (Click on image to see larger version.)

Crepe Ginger (Costus speciosus) – This species is a native of the Greater Sunda Islands of Indonesia and the Malay Peninsula. Although it has become naturalized in the Hawaiian Islands, its invasive tendencies enable it to crowd out native species. Its preferred habitat is moist fertile soils and partial sun, but will grow well in full sun if it gets plenty of moisture. One of the most cold-hardy of the gingers, it has been shown to withstand freezing temperatures as low as 17 degrees Celsius. Crepe Ginger is a tall and substantial-looking plant with large (15-30 cm long by 5-7 cm wide) dark-green leaves arranged on the stalk in a spiral. This species can grow to more than 3 m tall under ideal soil and climatic conditions. The unusual-looking flowers bloom throughout the year in tropical climates, but only in late summer to early fall in colder conditions. The flower’s single ,petal (actually the male part of the flower) looks like crepe paper, hence the common name “Crepe Ginger”. This and other ginger species propagate most effectively by producing a large network of thick fleshy rhizomes that are similar in appearance to the “ginger root” sold in grocery stores and at farmer’s markets. A single rhizome will produce new shoots and grow into a clump more than one meter in diameter in less than two years. Traditionally, the  rhizome has been used to treat fever, rash, asthma, bronchitis, and intestinal worms. In India and Southeast Asia, this species is still used to treat boils, constipation, diarrhea, dizziness, headache, and vertigo (“seasickness”). This species is also a source of diosgenin, a compound used for the commercial production of clinically important steroids such as progesterone.

White Ginger (Heydychium coronarium), Hana, east Maui. (Click on image to see larger version.)

White Ginger, Ginger Lily (Hedychium coronarium), Hawaiian = `awapuhi ke`oke`o – A native of India, it was exported throughout the tropics because of its popularity as an ornamental species. It soon escaped the confines of private gardens and became naturalized throughout the Hawaiian Islands. It is considered an invasive weed because of its ability to propagate quickly by sending out many shallow roots (rhizomes) in all directions, creating dense thickets of individual plants. This creeping growth quickly overwhelms and crowds out other low-growing plant species. Hedychium coronarium is a perennial herb that can grow as two meters in height. It prefers moist habitats, such as rain forests, the banks of streams, moist forest, roadsides, and open fields and pastures. It has large (30 cm long by 10 cm wide at maturity) simple elliptical or lance-shaped leaves.  It produces large numbers of flowers throughout the year. The fragrant white flowers are borne on long (10-20 cm) elliptical spikes in groups of two to six flowers atop a leafy stem.  The fruit is borne in an oblong many-seeded capsule, but is not usually present or easily seen since propagation of the species is usually accomplished by spreading rhizomes.

Indonesian Wax Ginger (Tapeinochilos ananassae). Flower head is about 25 cm long. Well adapted to the moisture and shade of Maui’s rain forests.
(Click on image to see larger version.)

Indonesian Wax Ginger or Pineapple Ginger (Tapeinochilos ananassae) – Like other ginger species growing in Hawaii, this plant was introduced for its ornamental attributes: a large, showy inflorescence and beautiful foliage. Its foliage consists of thick, jointed bamboo-like stems that grow directly from numerous rhizomes. The long, smooth, lance-shaped leaves are arranged on the stem in an inward-curving spiral typical of this species; the leaves radiate outward from the spiral.  The small yellow flowers (which function as attractors to pollinating insects and birds) are aggregated in a large (10-30 cm long), bright-red pineapple-shaped terminal spike consisting of what appear to be waxy bright red flower petals, but are actually bracts (modified leaves that enclose the actual flower). To reach its full height (about 3 m), this species requires very high humidity. It prefers the full shade and moist, fertile, well-drained soils of the rain forest. Unlike many other tropical ginger species, this plant possesses no aromatic essential oils.

Scarlet Spiral Flag Ginger (Costus woodsonii), Hana Maui Botanical Gardens, east Maui.
(Click on image to see larger version.)

Scarlet Spiral Flag Ginger, Indian Head Ginger, or Red Button Ginger (Costus woodsonii Maas), Hawaiian: ‘awapuhi ‘inikini po‘o – This species has gently spiraled stems and grows to about a meter in height. The leaves are deep green. The bracts of the inflorescence are bright waxy red, forming a pine cone-like spike (10-15 cm long) from which the yellowish-orange flowers protrude outward one at a time. The numerous small black seeds (1-2 mm long, the smallest of the true gingers) are usually dispersed by birds, but it is possible that they are also dispersed by water if the plant is growing in a wetland environment. C. woodsonii is an aggressive and invasive species. Its rhizomes spread rapidly and, once established, they are difficult to remove.  This species grows well in full sun, flourishing even in the sandy soils and dune sands of tropical coasts, but it prefers the shade, ample moisture, and deep, fertile soil of the rain forest. Although the genus Costus sp. is found throughout the tropics on all continents, this species was first collected and described in Panama in 1941. It was an introduced ornamental garden plant that became a naturalized escapee in some parts of Hawaii. It is considered to be an invasive weed on Oahu, Maui, and Kauai islands. It is present in large but widely scattered populations at low elevations on Maui, particularly along the Hana Highway. This species also displays a classic behavior of species mutualism: it exudes what is known as “extrafloral nectar” from the bracts of the flower spike, attracting ant species that harvest the nectar. In turn, the ants protect the plant from the larvae of flies and other flying insects that lay their eggs in the flowers.

The pink variant of Red Ginger (Alpinia purpurata), a garden in Kihei, south Maui. (Click on image to see larger version.)

Red Ginger (Alpinia purpurata), Hawaiian = ‘awapuhi ‘ula‘ula – Originally a native of Southeast Asia, A. purpurata was introduced to Hawaii as an ornamental species in 1928; it is now naturalized. Grows to about 3 m tall in the wild (can grow to more than 9 m tall under cultivation) and forms large clumps of foliage bearing large oblong leaves (30-80 cm long by more than 20 cm wide).  As with other ginger species, the large inflorescence (15-30 cm long, getting longer as the plant ages) consists of brightly colored (usually pink or red, occasionally white) bracts that look like a bloom, but the true flower is a small white blossom (corolla) at the outermost tip of the inflorescence. The fruit is a globular seed capsule about 3 cm in diameter that contains numerous small seeds (2-3 mm long). Although this species of ginger will tolerate direct sunlight, it requires very high humidity and soil moisture, as well as warmer air temperatures (more than 50 degrees F) to grow to its full size. Research has revealed that this species is a possible natural source for bioactive compounds useful for the treatment of hypertension.

The Coconut Palm: A Hawaiian Icon

My introduction to the Islands, long before I came to my Hawai’i nei, was a peeled coconut I bought in a local grocery store in California. The first thing I noticed was the three conspicuous round depressions at one end of the nut. My Dad said they were the coconut’s eyes. Fifty years later I read that these “eyes” were actually the germination pores out of which a root-sprout eventually appears. About the same time I discovered this old Hawaiian belief: Coconuts have eyes so they can see where they fall and so never fall on anyone. I like that explanation better…

Coconut endocarp (shell) displaying the three characteristic germination pores or “eyes.”

The Coconut Palm (Cocos nucifera) is a member of the family Arecaceae (palm family). The genus name “Cocos” may have come from a Portuguese word meaning “monkey”, perhaps because its nut, bearing three germinating pores, resembles a monkey’s face. Its species name is derived from the Latin phrase meaning “nut-bearing” (that is, fero = “I bear” and nux-nucis = “nut”). In English, it is referred to as “coconut”, “cocoanut”, and “coconut palm”, all of which stem from the name of the fruit, not so much the tree itself. In Polynesian and Melanesian languages it is called “niu”, which is derived from the Malay words “nyiur” or “nyior”. This derivation may indicate that the species originated in the Malay-Indonesian region.

Distribution

The Coconut Palm is found in all tropical and subtropical regions 25 degrees north and south of the equator. Its distribution includes most of the world’s tropical islands and coastal regions. Rarely its range extends outside the tropics, where it will flower, but fruits fail to develop normally. Cocos nucifera is believed to have originated in the coastal areas of Southeast Asia (Malaysia, Indonesia, Philippines). In prehistoric times a wild precursor may have been carried eastward on ocean currents to the tropical Pacific islands (Melanesia, Polynesia, and Micronesia) where they established themselves on abundant sandy and coralline coasts. More than four thousand five hundred years ago, Polynesians migrating into the tropical regions of the Pacific Basin probably carried select aboriginal coconut species (“niu vai”) with them on their ocean-going canoes. Some researchers believe that the tree originated along the northwestern coast of South America. There is fossil evidence (more than 15 million years old) of small coconut-like plants in New Zealand and the Indian Subcontinent. Regardless of its origin, the Coconut Palm has spread inland (with the help of migrating humans) and flourishes in a wide variety of soil types and at altitudes in excess of 600 meters (1,970 feet) above sea level. Although it is considered to be a non-native species in the Hawaiian Islands, there is no danger of the Coconut Palm becoming an invasive nuisance species because the large size and low numbers of fruits produced by a single tree restrict its ability to spread uncontrollably.

Mature coconut palms, Kalepolepo Beach, Maui. (Click on image for a larger version.)

Description

Of the two major classes of coconut palms, tall (average height at maturity is 18 m) and dwarf (average height 6 m), the tall variety is most common; and so, for the purposes of this blog, all my descriptions refer to that variety.

A nice stand of mature trees, Keanae Village, Maui. (Click on image for a larger version.)

Growth Rate – A Coconut Palm will grow continuously throughout the year under ideal environmental conditions (uniform soil moisture, high humidity and air temperature). The tall variety of Coconut Palm is slow to mature, setting flowers six to ten years after planting. During the first 40 years of a tree’s life it averages 30 to 50 cm of growth annually. After about four years, the majority of growth occurs in the trunk. Fruit production increases after the sixth year at the expense of vegetative growth. Thereafter, growth is fairly constant as fruit yields are sustained for the next 40 years. The average lifespan of the tree is 60 to 70 years, but some trees live more than 100 years.

Immature coconuts; note the green exocarp (skin).  (Click on image for a larger version.)

Tree – The bark of the solitary trunk is smooth, colored ash-gray to almost white, and marked by numerous ring-shaped scars left by the basal attachments of leaves that have fallen as the trunk grows in height. The strong yet very flexible trunk enables the tree to bend freely in heavy wind. There are numerous stories of people stranded during tropical storms lashing themselves to the trunks of mature coconut palms to prevent being washed out to sea. It is not unusual to see trunks of mature trees that are leaning over at a precarious angle or that have been noticeably contorted: this is usually due to the tree reaching upward for greater exposure to sunlight. More extremely misshapen trunks are caused by nutritional deficiencies.

Ripening coconuts; note yellowish-brown exocarp. (Click on image for larger version.)

Leaves — Until about the end of the first year of growth, the leaves remain entire (that is, not divided into leaflets as in a mature tree). Thereafter, the leaves become progressively more pinnate (shaped like a bird’s feather). The full crown of the mature tree carries numerous (usually 20 to 30) leaves (referred to as “fronds”) that can be as much as 20 feet long and bear 200 to 250 dark-green, slightly recurved leaflets about one meter long. The petiole (or “stem”) of the frond takes up about 25 percent of the total length of the frond. The large base of the petiole provides a strong attachment for the frond to the trunk. Leaves remain attached to the tree’s crown for about 2.5 years after unfolding, whereupon they “senesce” (drop off), leaving the distinctive ring-like scar on the trunk.

Root System — Unlike most trees, a Coconut Palm has no tap root or root hairs. Instead the root system consists of  2,000 to 4,000 adventitious roots about one centimeter in diameter. The depth to which the roots extend depends on the soil type and depth to the local water table. Individual roots can grow to depths of five meters, the majority of the tree’s root system is concentrated in the upper 1.5 meters of the soil. Lateral growth averages six meters, but under ideal conditions will extend as far as 30 m outward from the base of the trunk.

The male and female flowers of a mature tree.

Flowers — The Coconut Palm produces flowers 12 to 15 times a year. This species is monoecious: that is, it includes male and female flowers on the same inflorescence (a flower spike or “spadix”) that develops within a woody sheath (spathe). When flowering occurs, the spathe splits lengthwise, exposing the spadix. Each orange to straw-colored spadix is 1 to 1.5 m (3.3 to 5 ft) long with 40 to 60 branches (or spikelets) bearing the flowers. Each spikelet may carry as many as three female flowers (buttons) at its base and several hundred male flowers above. As a result, a spadix may carry several thousand male flowers but only 40 to 60 buttons. Coconut Palms are cross-pollinated, either by anemophily (pollen is carried on the wind) or entomophily (pollen is distributed by insects). However, pollination can occur between flowers of successive spadices on the same tree. A tree’s first flowering may occur at four to five years of age. When the tree reaches maturity, a spadix (flower spike) is produced on every leaf. Twelve to fifteen spadices (per leaf) are produced annually at regular intervals. Drought conditions can delay emergence of the spadix or cause it to abort. The number of female flowers per spadix varies, governed by environmental conditions.

A recently fallen coconut; note the greyish-white color of the exocarp. (Click on image for a larger version.)

Fruit (the “coconut”) — Each coconut fruit (technically not a true nut, it is known as a “fibrous drupe”) is about the size of a bowling ball and weighs more than two kilograms. Because it is relatively light and very buoyant, a fruit that is dropped in water or carried away on an incoming tide can be borne by ocean currents for a great distance and still be viable enough to germinate. Fruits that have remained in seawater for as much as 120 days are still able to germinate and take root successfully. A mature tree produces 50 to 80 fruits throughout the year. Roughly 40 percent of set fruit are carried to full term within three months of pollination. Although it takes 15 months from flowering for the fruit to mature, the drupe is usable (the water in the endocarp is fit to drink) at about five months.

Immature coconut sliced open to show mesocarp (“coir”) and endocarp (“shell”). (Click on image for a larger version.)

Hawaiian names for the various stages of coconut fruit development:

• ‘o ‘io – Unripened fruit contains jelly-like translucent flesh you can eat with a spoon.
• hao hao – Almost half matured with shell still white and flesh is soft and white.
• ho ‘ilikole – Half-ripe, meat eaten raw with red salt and poi.
• niu o‘o – Fruit is mature but the husk has not dried.
• niu malo‘o – Fruit is mature, the husk is dry, water still present; best stage for planting; used to make coconut cream, which when mixed with kalo/taro makes a dish called kulolo; with `uala/sweet potato it is called poipalau; and paipaie’e with ripe `ulu/breadfruit. The mature meat of coconut is also grated, squeezed or scraped to be cooked in main dishes with fish, chicken or greens.
• niu ka‘a – Old fruit with no water and flesh separated from shell; coconut oil is extracted at this stage.

Endocarp (shell) cracked open to show solid portion (“meat”) of the endosperm. (Click on image to see a larger version.)

Parts of the Fruit

The exocarp is the thin outermost layer (or skin) of the fruit. The mesocarp is a thick husk composed of coarse brown fibers (coir). The endocarp is the hard, but relatively thin woody inner layer of a fruit that contains the endosperm. The endosperm is partly liquid (“coconut water”) and partly solid (fibrous white coconut “flesh” or “meat”, which adheres to the inner wall of the endocarp). The liquid portion of the endosperm is rich in minerals, vitamins, Lauric (fatty acid-based) oils, and carbohydrates. The minute embryo (or seed) is embedded in the solid fleshy portion of the endosperm just inside one of the three germination pores (called “eyes”) through which the radicle (the embryonic root of the seedling) emerges when the embryo germinates.

A fallen coconut displaying the fibrous coir (mesocarp). (Click on the image to see a larger version.)

Coconut Water – This is the clear liquid portion of the endosperm. When the coconut is about six to seven months old, the water is ready to drink; the coconut is full-sized, but is still green with no trace of yellow on the exocarp. This is the point in the growth cycle when the jelly-like flesh of the endosperm begins to solidify. The coconut should be picked by hand, not fallen from the tree. At this point there is about one liter of liquid in the coconut, but you can’t hear it inside the fruit when shaken. The water is at its sweetest and it is lowest in acidity, and can only be stored for about two days. The characteristics of the water change as the fruit matures: an immature coconut 3 – 5 months old (before the endosperm begins to form) has tasteless water that is somewhat astringent; the water of a mature coconut has a slightly salty taste and is more acidic.

Coconut Milk –  This should not be confused with coconut water. When a mature coconut drops off the tree, it still contains some of the liquid endosperm. This can be combined with grated coconut meat to make coconut milk. It has a fat content of approximately 17 percent. The milk is used to produce virgin coconut oil by means of fractionation (a closely controlled heating process); when the process is completed, the oil fraction is drawn off.

A fallen coconut germinated in volcanic soil.

Preferred Environment

Soils – The Coconut Palm is capable of adapting to a remarkable variety of soil types, from very coarse or gravelly soil to clay, as long as they possess good drainage and aeration. It does not tolerate oversaturated soil within about one meter of the surface, and will not survive more than two weeks of surface water-logging. Although coarse sand is its preferred soil type, it will grow readily in loamy soils as well as clay soils that are well drained. It is very tolerant of soils with high salinity and is not bothered by salt spray. It tolerates alkaline soils with a pH of 8 and acid soils with a pH of more than 4.5. Its preferred pH range is 5.5 – 7.

Climate – Obviously a plant of the tropics, the Coconut Palm prefers a year-round warm and humid climate characteristic of the coasts of large landmasses and islands where the sea exerts a moderating influence on temperature and humidity. A mean annual temperature of 27°C (81°F), evenly distributed annual rainfall of 1500 to 2500 mm (60 -100 in), and high relative humidity (more than 60 percent) are the ideal climatic conditions for the healthy growth and propagation of the palm. A permanent water table within easy reach of its roots can make up for inadequate rainfall, while annual rainfall in excess of 2500 mm (100 in) render the tree vulnerable to diseases of the leaves and fruit. The Coconut Palm does not tolerate low temperatures and will not survive in sustained temperatures much below 2°C (36°F). However, some seasonal variation is tolerated: it will survive brief periods of freezing temperatures (0 to -4 °C), but severe frost is usually fatal. It also does poorly under sustained drought conditions. Symptoms of drought-induced stress include desiccated older fronds, new fronds that fail to open normally, and the premature shedding of immature fruits. Though it prefers to grow in full sunlight, the Coconut Palm will tolerate some shading by other trees, but it is slow to mature and produces fewer fruits under heavily-shaded conditions. If the tree’s root system is well anchored, it is able to withstand hurricane-force winds with ease. The innate flexibility of the tree’s trunk and fronds reduces its cross-sectional area and lowers the drag forces to which it is subjected during high-wind conditions.

Coconut Palm Products and Uses

In those parts of the world where the Coconut Palm grows naturally and is widely cultivated, indigenous people have learned to make use of nearly every part of the tree. For thousands of years, the “people of the coconut palm” have learned to use the trunk wood and roots, foliage, flowers, and fruit of the tree to fashion tools, weapons, hardware, building and clothing materials, and decorative and religious works of art. From the meat, oil, milk, and water of the coconut’s fruit they have produced an astonishing menu of appetizing and nutritious food items, as well a voluminous pharmacopeia of traditional medicines and treatments.

A note about the uses of Cocos nucifera in the Hawaiian Islands – The Hawaiian Islands are located on the northernmost edge of what may be called the “Coconut Belt”. In the islands and continental regions that are closest to the equator, the Coconut Palm is more numerous and productive of its fruits, and so it was and is more widely used there than in Hawai`i. Here there have always been other plants, native and introduced, that provide as well for people’s needs, and so the Coconut Palm plays a somewhat subordinate role in Hawaiian culture. However, Niu was considered to be such a valuable plant that it was included as cargo on the crowded sailing canoes of the original Polynesian voyagers who colonized Hawai`i Nei. For this reason, and because Cocos nucifera has become so emblematic of the Hawaiian Islands and is such a visible presence here, the Coconut Palm enjoys a popularity (and even a kind of reverence) here in the Islands that is out of proportion to its actual role in Hawaiian history and culture.