Arecaceae
Arecaceae (palm family)
CoconutPalm
Cocos nucifera
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Liliopsida
Order: Arecales
Family: Arecaceae
Genera
Arecaceae (also known as Palmae or Palmaceae), 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 or subtropical
climates. Of all the families of plants, the Arecaceae is the most
easily recognizable as distinct by most persons. 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
plants. They have had an important role to humans throughout much of
history, starting with the ancient Mesopotamians. 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, universal symbol for the tropics and
vacations [1].
Characteristics and evolution
Range
The overwhelming majority of palms live in the tropical latitudes
between 23.5°N and 23.5°S. Palms are abundant throughout the
tropical regions of every continent except Antarctica, 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 [2].
It is estimated that only 130 palm species grow naturally beyond the
tropics, most of which grow in the subtropics. The northernmost palm
is Chamaerops humilis, which reaches 43°N latitude in southern
France where a mediterranean climate makes weather 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 [3].
Morphology and habitat
Washingtonia filifera grove in Palm Canyon, California
The growth habit of palms is usually a straight, unbranched stem,
and rarely a dichotomous branching stem or a creeping vine-like
habit (liana) [4]. 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 [5]. 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 may
be bisexual or unisexual. 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 berry or drupe [6].
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 [7]. 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 montane 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 [3].
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 [2].
Taxonomy
Palms are a monophyletic group of plants, meaning that the group
consists of a common ancestor and all its descendants [7]. 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
[8]. 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 does not 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 [9].
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 is 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 [9].
Evolution
Arecaceae is the first modern family of monocots that is 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 Acromia
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 intrafamilial 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 [10].
Conservation
Pritchardia affinis, a critically endangered species endemic to the
Hawaiian Islands.
Unfortunately, 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 is 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 [11]. The sale of seeds to nurseries and
collectors is another threat, and 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 [7].
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, but
they cannot 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 and
cannot truly imitate the natural setting [12].
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 [12].
Uses and cultivation
Fruit of the Date Palm Phoenix dactylifera
Human use of palms is almost as old as human civilization itself,
starting with the cultivation of the Date Palm by Mesopotamians 5000
years ago. Date wood, pits for storing dates, and other remains of
the Date Palm have been found in Mesopotamian sites.[13] Palms are
mentioned at least 30 times in the Bible[14]. 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 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 [15]. 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
[16].
Washingtonia robusta trees line Ocean Avenue in Santa Monica,
California.
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 [17]. 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.[18] 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[19]. The Chinese Trachycarpus fortunei is being
grown experimentally on the Faroe Islands at 62°N, with young plants
doing well so far [20].
Symbolism
Waving palm leaves to welcome Christ into Jerusalem
The palm branch was a symbol of triumph and victory in pre-Christian
times. The Romans rewarded champions of the games and celebrated
military successes with palm branches. In fact, the motto of the HMS
Nelson was "Palmam qui meruit ferat", which means in Latin, "Let him
bear the palm who has deserved it".[21] Jews followed a similar
tradition of carrying palm branches during festive times.[22] 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
Christian art, martyrs were usually shown holding palms representing
the victory of spirit over flesh, and it was widely believed that a
picture of a palm on a tomb meant that a martyr was buried there.
[23] Palms also represented heaven, evidenced by ancient art often
depicting Jesus in heaven among palms. Today, the palm, especially
the Coconut, remains a symbol of the stereotypical tropical island
paradise [7].
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. The sacred tree in Assyrian mythology is a palm that
symbolizes Ishtar connecting heaven, the crown of the tree, and
earth, the base of the trunk. Muhammad supposedly built his home out
of palm, and the palm symbolizes rest and hospitality in many
cultures of the Middle East. Palm stems represented long life to the
Ancient Egyptians, and the god Huh was often shown holding a palm
stem in one or both hands. The palm tree was a sacred sign of Apollo
in Ancient Greece because he had been born under one in Delos [24].
In ancient Mesopotamia, the Date Palm may have represented fertility
in humans. The Mesopotamian goddess Inanna, who had a part in the
sacred marriage ritual, considered herself the one who made the
dates abundant [13].
Palms appear on the flags and seals of several places where they are
native, including those of Haiti, Guam, Florida, and South Carolina.
Economically important genera
Areca Betel palm
Bactris Pupunha
Borassus Palmyra palm
Calamus Rattan palm
Cocos Coconut
Copernicia Carnauba wax palm
Elaeis Oil palm
Euterpe Cabbage Heart palm, Açaí palm
Jubaea Chilean Wine palm, Coquito palm
Metroxylon Sago palm
Phoenix Date palm
Raphia Raffia palm
Roystonea Royal palm
Sabal Palmettos
Salacca Salak
Trachycarpus Windmill palm, Kumaon palm
Washingtonia
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