Palms are long-lived, woody monocotyledons that are solitary or clumping in growth habit, bear a distinctive crown of leaves, produce unisexual or bisexual flowers on the same or separate plants, and reproduce by seeds (see Chapter 3, Article 1). They represent a monophyletic group* of plants of the Family Palmae (alternative name Arecaceae) and of the order Arecales (see Chapter 3, Article 3). Although palms generally have a characteristic appearance that allows most people to easily recognize them, several unrelated plant groupssuch as the cycads (the king sago, Cycas revoluta, the queen sago, Cycas circinalis, and the cardboard palm, Zamia furfuracea), the cyclanths (Panama hat palm, Carludovica palmata), the pandans (screw palms, Pandanus sp.), and the agaves (ponytail palm, Nolina recurvata)bear a superficial resemblance and are sometimes called palms. Also incorrectly called a palm is the travellers palm, Ravenala madagascariensis, which is in the bird-of-paradise family, Strilitziaceae.
The palms are ancient land plants, with fossils dating as far back as the late Cretaceous (~85 million years before present [mybp]). Because they are composed of durable materials, palms have a relatively good fossil record (see Chapter 5). For example, pollen grains from the mangrove palm, Nypa fruticans, have been found in Eocene sediments (~50 mybp) near London. Also present in these same sediments is pollen from a rattan palm, Calamus daemonorops, fruit of an Oncosperma and a Sabal, and seeds similar to those of the fishtail palms, Caryota.
Many people regard palms as the princes of the plant kingdom. In fact, the great Swedish botanist Carolus Linnaeusthe founder of the modern binomial system of biological nomenclaturelabelled them as Principes. Today, Principes (recently changed to PALMS) is the name of a popular scientific journal published by the International Palm Society.
The palms are highly speciose, with an estimated 2500-3500 species in 210-236 genera (see Chapter 4). Variation in species numbers arises from disagreement between botanists as to the delineation of species and genus boundaries. Regardless of the exact number of species, palms comprise a significant and diverse group that ranks fourth or fifth in size (depending on which species estimate is used) in the monocotyledons.
Although diverse, variations in palms arise around a basic theme of being perennial, unisexual or bisexual woody plants with a distinctive crown of leaves at the aerial growing end and adventitious roots at the subterranean growing end. Most species have a prominent, or even massive solitary trunk (termed monopodial; Elaeis guineensis, Roytonea sp., Copernicia baileyana, Corypha umbraculifera), but a few have trunks that grow along the ground (termed prostrate or decumbent; Elaeis oleifera, Serenoa repens), and even fewer appear to be trunkless (termed acaulescent; Raphia regalis, Salacca sp., most Johannesteijsmannia species). A significant number of species produce new shoots from axillary buds at the base of the stem, forming clumps or clusters (termed sympodial; some Areca species; some Chamaedorea species; Rhapis), a few species are climbers (Chamaedorea elatior, Calamus sp., Korthalsia sp., Daemonorrops sp., Plectocomia sp.), and a few have dichotomously branching trunks (Nypa fruticans, Hyphaene sp., Chamaedorea cataractum, Allagoptera arenaria). Although the growth habit is usually characteristic for a particular group, sometimes both clumping and solitary habits may be present in one genus (Licuala, Hyphaene, Ptychosperma) or even within a species (Laccospadix australasica, Dypsis pembanus).
Palm leaves are prominent and have a characteristic shape, usually either palmately or pinnately compound, although one genus is exclusively binnate (Caryota). The crown of leaves is usually characteristic within a species, ranging from numerous and dense (Chamaedorea cataractum, Copernicia baileyana) to few and sparse (Hyophorbe lagenicaulis, Gaussia attenuata). The African raffia palm, Raphia regalis, has the longest leaves in the plant kingdom, extending up to 25 meters (83 feet) from the acaulescent trunk.
Palms flower when they are mature, which occurs in some species in as little as 3-5 years (Veitchia sp., Elaeis guineensis), while other species take more than 40 years to mature (Corypha umbraculifera). Most species flower regularly throughout their entire adult life (termed pleonanthic) by producing inflorescences from successive nodes up the trunk (termed acropetal flowering). However, some specialized palms, such as Arenga pinnata and Caryota urens, exhibit a restricted flowering process in which the inflorescences are produced down the stem (termed basipetal flowering) over a period of timeperhaps yearsand then the whole plant dies when the lowermost bunch of fruit ripens. When this occurs in clumping species, such as Arenga tremula and Caryota mitis, individual stems die (termed hapaxanthic) but the mat remains alive as suckers shoot up from the base to replace lost stems. Monocarpic palms produce a single, terminal inflorescence once in their lifetime and then die. The most famous of these is the talipot palm, Corypha umbraculifera, which has the largest inflorescence of any species in the plant kingdom, rising nearly 10 meters (33 feet) from the top of the plant and bearing several million flowers.
Palm flowers are generally small and individually inconspicuous, but they are often produced enmasse and can be quite showy. Palm seeds usually have a hard seed coat and are often surrounded by a colorful fleshy mesocarp, which makes up the fruit. The seeds of most species can germinate on maturityand often have a very short shelf lifebut some may have an after-ripening mechanism. The largest seed in the plant kingdom is that of the double coconut, Lodoicea maldavica, with individual seeds weighing as much as 20 kg (44 lbs.).
The stereotypical tropical paradise of a small island or a stretch of white sand beach with overhanging coconut palms is appropriate, since palms reach their greatest proliferation in the tropics and are widely distributed in warmer zones of the world with high levels of rainfall. Where they occur, palms can be a dominant component of the vegetation. Despite the wide familial distribution and frequency of palms in the tropics, few genera have many species and/or are widespread. In fact, most palm genera contain five or fewer species and monotypic genera are common. Many of the smaller genera have a worldwide distribution, whereas some larger genera have proliferated in relatively restricted areas. Examples of the former are Phoenix, Borassus, and Raphia, and of the latter are Licuala and Pinanga, each with over 100 species restricted to the area between Malaysia and New Guinea, and Chamaedorea, with 100 species restricted to Central and South America.
More than two-thirds of the worlds palm species grow in rainforests, where they may be emergent plants with their crowns well above the forest canopy, intermediate-sized plants that mingle with the canopy but do not emerge, or small understorey plants growing in deep shade on the forest floor. Some of the hardiest species, like the date palm, Phoenix dactylifera, live in dry open habitats like savannah grasslands, but even these must have access to a permanent underground water source. Other hardy palms include Nannorrhops ritchiana, which lives in the mountains of Afghanistan, and Trachycarpus species in the Himalayas, which are regularly covered with snow each winter.
As with any large group of plants, palms contain unusual and interesting oddities. As stated above, the largest seed, the largest inflorescence, and the longest leaf of all plants belong to palms. One species, the mangrove palm (Nypa fruticans) is a significant component of mangrove communities in estuaries in Asia and the western Pacific. Another species, Ravenea musicalis from Madagascar, is truly aquatic, growing in fast-flowing streams in water up to 2.5 m (8 ft) deep; the seeds germinate within the fruit and the second and third scale leaves have a hooked apex which catches on protuberances on the stream bed, thus anchoring the seedling. Palms range in size from the diminutive Paraguayan lilliput palm, Syagrus lilliputiana (thought to be extinct), that measures 10-15 cm (4-5 in) tall at maturity to the giant wax palms of the Andes (Ceroxylon quindinense and C. alpinum) and the wanga palm of New Guinea (Pigafetta filaris), which can reach 60 m (197 ft) and 50 m (164 ft), respectively.
Many groups of plants have been detrimentally affected by human activities, and palms are no exception (see Chapter 7). The greatest threat to palms is destruction of habitat, which has occurred, or continues to occur in most countries where they are native. Large-scale operations such as forestry, wood-chipping, mining, conversion of land to farms, and shifting agriculture pose major threats; ironically, palms are often left alone during these operations but can rarely reproduce in the drastically altered aftermath. Many palm species have been forced to the brink of extinction by the collection of cabbage (palm heart is considered a delicacy), of leaves for thatch or animal fodder, and, more recently, of seeds for sale to nurseries and palm enthusiasts. Also ironic is the increasing commonality of species such as the bottle and spindle palms (Hyophorbe lagenicaulis and H. verschefeltii) and the blue, red, and yellow latans (Latania loddigesii, L. lontaroides, and L. verschefeltii) in the nursery trade, when their wild populations in the Mascarene Islands have been reduced to only a few isolated individuals. At least 100 species are currently recognized as endangered, although this figure is unfortunately only preliminary. (See D. V. Johnson, World Endangerment of Useful Palms in the Palm Tree of Life, Advances in Economic Botany (1986):268-273.)
Jones (1995) reported that nine palm species were thought to have recently gone extinct, mainly as a result of urbanization and habitat disturbance/destruction: Sabal miamiensis, described in 1985 in Florida; Roystonea stellata from Cuba; Pritchardia macrocarpa and P. montis-kea from Hawaii; Syagrus leptospatha and S. macrocarpa from Brazil; Syagrus lilliputiana from Paraguay; Thrinax ekmaniana from Cuba; and Medemia argun from oases in Egypt and Sudan. Since Palms Throughout the World was published, Medemia argun has been rediscovered in Sudan and this species has been introduced into the nursery trade by Martin Gibbons of The Palm Centre. Chuck Hubbuch (pers. comm.), Director of Collections at Fairchild Tropical Garden, recently noted that Sabal miamiensis is also not extinct, but is quite rare in the wild; several mature specimens are currently growing at Fairchild. Further, Carlo Morici (pers. comm.), of Palmetum de Santa Cruz de Tenerife (Palmetum), claims that Thrinax ekmaniana is also not extinct but is very rare, with only about 200 plants surviving in the wild in a localized area of Cuba. Morici further stated that T. ekmaniana is not considered endangered, being actively protected and surveyed by the Cuban government, but is very rare in cultivation. Morici collected seeds two years ago and distributed hundreds to other botanical gardens; the Palmetum is currently growing seven plants. Morici also recently informed me that the Palmetum is involved in ongoing efforts to rescue the possibly extinct R. stellata in Cuba.
Unfortunately, the number of species becoming threatened, endangered, or extinct is likely to increase in coming years due to widespread devestation in places like Madagascar, which has probably the largest flora of endemic palms in the world, as well as elsewhere around the world. Any efforts that you and I can do to help out are, and will be, greatly appreciated!
*A monophyletic group is a group of taxa (species, genera, families, etc.) descended from a single common ancestor and which includes this single common ancestor and all descendent species or higher level groups; also called a true group.
References used for this chapter:
Jones, D. L. 1995. Palms Throughout the World. Smithsonian Institution Press, Washington, D. C.
Stewart, L. 1994. A Guide to the Palms & Cycads of the World. Angus & Robertson, Sydney, Australia.
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