Everything about Arecaceae totally explained
Arecaceae or
Palmae (also known by the name
Palmaceae, which is taxonomically invalid), the palm family, is a family of
flowering plants belonging to the
monocot order,
Arecales. There are roughly 202 currently known
genera with around 2600
species, most of which are restricted to
tropical,
subtropical, and possibly warm
temperate climates. Most palms are distinguished by their large, compound,
evergreen leaves arranged at the top of an unbranched stem. However, many palms are exceptions to this statement, and palms in fact exhibit an enormous diversity in physical characteristics. As well as being morphologically diverse, palms also inhabit nearly every type of
habitat within their range, from
rainforests to
deserts.
Palms are one of the most well-known and extensively cultivated plant families. They have had an important role to humans throughout much of history. Many common products and foods are derived from palms, and palms are also widely used in landscaping for their exotic appearance making them one of the most economically important plants. In many historical cultures, palms were
symbols for such ideas as victory, peace, and fertility. Today, palms remain a popular symbol for the tropics and
vacations.
Morphology
Whether shrubs, trees or vines palms are limited to two methods of growth. The common representation is that of a solitary shoot ending in a crown of leaves. This
monopodial behavior may be exhibited in prostrate, trunkless and trunk forming members. Some of the common palm trees restricted to solitary growth include
Washingtonia and
Roystonea. Palms may instead grow in sparse to dense clusters. The trunk will develop an axillary bud at a leaf node, usually near the base, from which a new shoot emerges. The new shoot, in turn, produces an axillary bud and a clustering habit results. Exclusively
sympodial genera include many of the
rattans,
Guihaia, and
Rhapis. Several palm genera have both solitary and clustering members. Occasionally, a plant is very often clustering with the occasional solitary member or the converse. These aberrations suggest the habit operates on a single gene.
They have large evergreen
leaves that are either palmately ('fan-leaved') or pinnately ('feather-leaved') compound and spirally arranged at the top of the stem. The leaves have a tubular sheath at the base that usually splits open on one side at maturity . The
inflorescence is a
panicle or
spike surrounded by one or more
bracts or
spathes that become woody at maturity. The
flowers are generally small and white, radially symmetric, and can be either uni- or bisexual. The sepals and petals usually number three each and may be distinct or joined at the base. The stamens generally number six, with filaments that may be separate, attached to each other, or attached to the pistil at the base. The
fruit is usually a single-
seeded
drupe, but some genera (for example
Salacca) may contain two or more seeds in each fruit.
Arecaceae is notable for having the individual trees with the largest seed, largest leaf, largest inflorescence, as well as the tallest individual monocot. The
coco de mer (
Lodoicea maldivica) has the largest seeds of any plant, 40-50 centimeters in diameter and weighing 15-30 kilograms each.
Raffia palms (
Raphia spp.), with leaves up to 25 meters long and 3 meters wide, have the largest leaves of any plant. The
Corypha species have the largest inflorescence of any plant, up to 7.5 meters tall and containing millions of small flowers.
Ceroxylon quindiuense,
Colombia's national tree, is the tallest monocot in the world, reaching heights of 60 meters .
Range and habitat
The vast majority of palms exist in the
tropics. Palms are abundant throughout the tropical regions around the world, and are present in almost every type of habitat in the tropics. Diversity is highest in wet, lowland tropical forests, especially in ecological "hotspots" such as
Madagascar, which has more endemic palms than the entire continental
Africa.
Colombia may have the highest number of palm species in one country.
It is estimated that only 130 palm species grow naturally beyond the tropics, most of which grow in the
subtropics. The northernmost native palm is
Chamaerops humilis, which reaches 44°N latitude in southern
France, where the local
Mediterranean climate is milder than other places as far north. The southernmost palm is the
Rhopalostylis sapida, which reaches 44°S on the
Chatham Islands where an
oceanic climate has a similar warming effect . Palms have been known to grow as far north as
Ireland.
Palms inhabit a variety of habitats. Over two-thirds of palms live in tropical forests, where some species grow tall enough to form part of the
canopy and other shorter palms adapted to shade form part of the
understory . Some species form pure stands in areas with poor drainage or regular flooding, including
Raphia hookeri which is common in coastal freshwater swamps in West Africa. Other palms live in tropical mountain habitats above 1000 meters, such as those in the genus
Ceroxylon native to the
Andes. Palms may also live in grasslands and scrublands, usually associated with a water source, and in
desert oases such as the
Date Palm. A few palms are adapted to extremely
basic lime soils, while others are similarly adapted to very
acidic
serpentine soils .
Taxonomy
Palms are a
monophyletic group of plants, meaning that the group consists of a common ancestor and all its descendants . Extensive taxonomic research on palms began with botanist H.E. Moore, who organized palms into fifteen major groups based mostly on general morphological characteristics. The following classification, proposed by N.W. Uhl and J. Dransfield in 1987, is a revision of Moore's classification that organizes palms into six subfamilies . A few general traits of each subfamily are listed.
Coryphoideae is the most diverse subfamily and is a
paraphyletic group, meaning that all members of the group share a common ancestor but the group doesn't include all the ancestor's descendants. Most palms in this subfamily have palmately lobed leaves and solitary flowers with three, sometimes four
carpels. The fruit normally develops from only one carpel. Subfamily Calamoideae includes the climbing palms such as rattans. The leaves are usually pinnate; derived characters (
synapomorphies) include spines on various organs, organs specialized for climbing, an extension of the main stem of the leaf bearing reflexed spines, and overlapping scales covering the fruit and ovary. Subfamily Nypoideae contains only one genus and one species,
Nypa fruticans, which has large pinnate leaves. The fruit is unusual in that it floats, and the stem is dichotomously branched, also unusual in palms. Subfamily Ceroxyloideae has small to medium-sized flowers that spirally arranged, with a
gynoecium of three joined carpels. Arecoideae is the largest subfamily with six diverse tribes containing over 100 genera. All tribes have pinnate or bipinnate leaves and flowers arranged in groups of three, with a central pistillate and two staminate flowers. Phytelephantoideae is a
monoecious subfamily. Members of this group have distinct
monopodial flower clusters. Other distinct features include a gynoecium with five to ten joined carpels, and flowers with more than three parts per whorl. Fruits are multiseeded and have multiple parts .
Currently, few extensive phylogenetic studies of Arecaceae exist. In 1997, Baker et al. explored subfamily and tribe relationships using chloroplast
DNA from 60 genera from all subfamilies and tribes. The results strongly showed that Calamoideae is
monophyletic, and that Ceroxyloideae and Coryphoideae are
paraphyletic. The relationships of Arecoideae are uncertain but it's possibly related to Ceroxyloideae and Phytelephantoideae. However, hybridization has been observed among
Orbignya and
Phoenix species, and using chloroplast DNA in cladistic studies may produce inaccurate results due to maternal inheritance of the chloroplast DNA. Chemical and molecular data from non-organelle DNA, for example, could be more effective for studying palm phylogeny .
Selected genera
See list of Arecaceae genera arranged [listof Arecaceae genera|by taxonomic groups]] or [Listof Arecaceae genera by alphabetical order|by alphabetical order] for a complete listing of genera.
Evolution
Arecaceae is the first modern family of monocots that's clearly represented in the fossil record. Palms first appear in the fossil record around 80 million years ago, during the late
Cretaceous Period. The first modern species, such as
Nypa fruticans and
Acrocomia aculeata, appeared 69-70 million years ago, confirmed by fossil
Nypa pollen dated to 70 million years ago. Palms appear to have undergone an early period of
adaptive radiation. By 60 million years ago, many of the modern, specialized genera of palms appeared and became widespread and common, much more widespread than their range today. Because palms separated from the
monocots earlier than other families, they developed more intra familial specialization and diversity. By tracing back these diverse characteristics of palms to the basic structures of monocots, palms may be valuable in studying monocot evolution.
Conservation
Like many other plants, palms have been threatened by human intervention and exploitation. The greatest risk to palms is destruction of habitat, especially in the tropical forests, due to
urbanization, wood-chipping, mining, and conversion to farmland. Palms rarely reproduce after such great changes in the habitat, and palms with a small habitat range are most vulnerable to them. The harvesting of
heart of palm, a delicacy in salads, also poses a threat because it's derived from the inner core of the tree and thus harvesting kills the tree. The use of rattan palms in furniture has caused a major population decrease in these species that has negatively affected local and international markets as well as biodiversity in the area. The sale of seeds to nurseries and collectors is another threat, as the seeds of popular palms are sometimes harvested directly from the wild. At least 100 palm species are currently endangered, and nine species have reportedly recently become extinct.
However, several factors make palm conservation more difficult. Palms live in almost every type of habitat and have tremendous morphological diversity. Most palm seeds lose viability quickly, and they can't be preserved in low temperatures because the cold kills the embryo. Using botanical gardens for conservation also presents problems, since they can only house a few plants of any species or truly imitate the natural setting. There is also the risk of cross-pollination,, which leads to hybrid species.
The Palm Specialist Group of the
World Conservation Union (IUCN) began in 1984 and has performed a series of three studies in order to find basic information on the status of palms in the wild, utilization of wild palms, and palms under cultivation. Two projects on palm conservation and utilization supported by the
World Wildlife Fund took place from 1985-1990 and 1986-1991, in the American tropics and southeast Asia respectively. Both studies produced a large amount of new data and publications on palms. Preparation of a global action plan for palm conservation began in 1991, supported by the IUCN, and was published in 1996 .
The rarest palm known is the
Hyophorbe amaricaulis. The only living individual that remains is at the Botanic Gardens of Curepipe in
Mauritius.
Uses and cultivation
Human use of palms is as old or older than human civilization itself, starting with the cultivation of the
Date Palm by
Mesopotamians and other Middle Eastern peoples 5000 years or more ago. Date wood, pits for storing dates, and other remains of the Date Palm have been found in Mesopotamian sites. The Date Palm had a tremendous effect on the history of the Middle East. W.H. Barreveld wrote:
» "One could go as far as to say that, had the date palm not existed, the expansion of the human race into the hot and barren parts of the "old" world would have been much more restricted. The date palm not only provided a concentrated energy food, which could be easily stored and carried along on long journeys across the deserts, it also created a more amenable habitat for the people to live in by providing shade and protection from the desert winds (Fig. 1). In addition, the date palm also yielded a variety of products for use in agricultural production and for domestic utensils, and practically all parts of the palm had a useful purpose.", and at least 22 times in the
Quran.
Arecaceae has great economic importance including coconut products, oils, dates, ivory nuts, carnauba wax, rattan cane, and raffia.
The type member of Arecaceae is the
Areca palm, the fruit of which, the
betel nut, is chewed with the
betel leaf for intoxicating effects. Also belonging to the family of the Arecaceae are the Date Palm, harvested for its edible fruit;
Rattans, whose stems are used extensively in
furniture and
baskets; and the
Coconut.
Palm oil is an edible vegetable oil produced by the
oil palms in the genus
Elaeis. Several species are harvested for
heart of palm, a vegetable eaten in salads. Palm
sap is sometimes
fermented to produce
palm wine or toddy, an
alcoholic beverage common in parts of
Africa,
India, and the
Philippines . The
Palm Sunday festival uses palm leaves, usually from the Date Palm, hence the name.
Dragon's blood, a red resin used traditionally in
medicine,
varnish, and
dyes, may be obtained from the fruit of
Daemonorops species.
Coir is a coarse water-resistant fiber extracted from the outer shell of
coconuts, used in doormats, brushes, mattresses, and ropes. Some indigenous groups living in palm-rich areas use palms to make many of their necessary items and food.
Sago, for example, a starch made from the pith of the trunk of the Sago Palm
Metroxylon sagu, is a major
staple food for lowland peoples of
New Guinea and the
Moluccas. Palm leaves are also valuable to some peoples as a material for thatching or clothing.
Today, palms are valuable as
ornamental plants and are often grown along streets in tropical and subtropical cities, and also along the
Mediterranean coast in Europe. Farther north, palms are a common feature in
botanical gardens or as indoor plants. Few palms tolerate severe cold, however, and the majority of the species are tropical or subtropical. The three most cold-tolerant species are
Trachycarpus fortunei, native to eastern
Asia, and
Rhapidophyllum hystrix and
Sabal minor, both native to the southeastern
United States . For more details, see
hardy palms.
The southeastern state of
South Carolina is nicknamed the Palmetto State after the
Cabbage Palmetto, logs from which were used to build the fort at
Fort Moultrie. During the
American Revolutionary War they were invaluable to those defending the fort, because their spongy wood absorbed or deflected the British cannonballs. Some palms can be grown as far north as
Maryland,
Arkansas, and even up along the Pacific coast to
Oregon,
Washington and
British Columbia, where ocean winds have a warming effect. There have even been known species of transplanted palms that have survived as far north as southern
New Jersey. The Chinese
Trachycarpus fortunei is being grown experimentally on the
Faroe Islands at 62°N, with young plants doing well so far.
Symbolism
The palm branch was a symbol of triumph and victory in pre-Christian times.Now it's popular symbol of the tropics and vacation. The
Romans rewarded champions of the games and celebrated military successes with palm branches. Early
Christians used the palm branch to symbolize the victory of the faithful over enemies of the soul, as in the
Palm Sunday festival celebrating the triumphal entry of
Jesus into
Jerusalem. In
Judaism, the palm represents peace and plenty, and is one of the Four Species of
Sukkot; the palm may also symbolize the
Tree of life in
Kabbalah. Today, the palm, especially the Coconut, remains a symbol of the stereotypical tropical island
paradise . Palms appear on the flags and seals of several places where they're native, including those of
Haiti,
Guam,
Florida and
South Carolina.
Further Information
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