Arecaceae Subtribes

The Arecaceae () is a family of perennial, flowering plants in the monocot order Arecales. Their growth form can be climbers, shrubs, tree-like and stemless plants, all commonly known as palms. Those having a tree-like form are colloquially called palm trees. Currently, 181 genera with around 2,600 species are known, most of which are restricted to tropical and subtropical climates. Most palms are distinguished by their large, compound, evergreen leaves, known as fronds, arranged at the top of an unbranched stem, except for the Hyphaene genus, who has branched palms. However, palms exhibit an enormous diversity in physical characteristics and inhabit nearly every type of habitat within their range, from rainforests to deserts.

Palms are among the best known and most extensively cultivated plant families. They have been important to humans throughout much of history, especially in regions like the Middle East and North Africa. A wide range of common products and foods are derived from palms. In contemporary times, palms are also widely used in landscaping. In many historical cultures, because of their importance as food, palms were symbols for such ideas as victory, peace, and fertility.

Etymology

The word ''Arecaceae'' is derived from the word ''areca'' with the suffix "-aceae". ''Areca'' is derived from Portuguese, via Malayalam അടയ്ക്ക (''aṭaykka''), which is from Dravidian ''*aṭ-ay-kkāy'' ("areca nut"). The suffix ''-aceae'' is the feminine plural of the Latin ''-āceus'' ("resembling").

''Palm'' originates from Latin ''palma'' semantically overlapping with sense of " hand front" (due to similar splayed shape) ultimately from Proto-Indo-European *''pl̥h₂meh₂'', a direct descendant once existed in Old English.

Morphology

Whether as shrubs, tree-like, or vines, palms have two methods of growth: solitary or clustered. The common representation is that of a solitary shoot ending in a crown of leaves. This monopodial character may be exhibited by prostrate, trunkless, and trunk-forming members. Some common palms restricted to solitary growth include ''Washingtonia'' and ''Roystonea''. Palms may instead grow in sparse though dense clusters. The trunk develops 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. Palms which are usually solitary may grow in clusters and vice versa.

Palms have large, evergreen leaves that are either palmately ('fan-leaved') or pinnately ('feather-leaved') compound and spirally (-alternately) arranged at the top of the stem, with the sole exception of the King Raphia ('' Raphia vinifera'' variety ''nigerica'') which has opposite pairs of fronds). The leaves have a tubular sheath at the base that usually splits open on one side at maturity. The inflorescence is a spadix 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 (sometimes berry-like) but some genera (e.g., ''Salacca'') may contain two or more seeds in each fruit.

Like all monocots, palms do not have the ability to increase the width of a stem (secondary growth) via the same kind of vascular cambium found in non-monocot woody plants. This explains the cylindrical shape of the trunk (almost constant diameter) that is often seen in palms, unlike in ring-forming trees. However, many palms, like some other monocots, do have secondary growth, although because it does not arise from a single vascular cambium producing xylem inwards and phloem outwards, it is often called "anomalous secondary growth".

The Arecaceae are notable among monocots for their height and for the size of their seeds, leaves, and inflorescences. ''Ceroxylon quindiuense'', Colombia's national "tree", is the tallest monocot in the world, reaching up to tall. The ''coco de mer'' (''Lodoicea maldivica'') has the largest seeds of any plant, in diameter and weighing each (coconuts are the second largest). Raffia palms ('' Raphia'' spp.) have the largest leaves of any plant, up to long and wide. The ''Corypha'' species have the largest inflorescence of any plant, up to tall and containing millions of small flowers. ''Calamus'' stems can reach in length.

Range and habitat

Most palms are native to tropical and subtropical climates. Palms thrive in moist and hot climates but can be found in a variety of different habitats. Their diversity is highest in wet, lowland forests. South America, the Caribbean, and areas of the South Pacific and southern Asia are regions of concentration. Colombia may have the highest number of palm species in one country. There are some palms that are also native to desert areas such as the Arabian Peninsula and parts of northwestern Mexico. Only about 130 palm species naturally grow entirely beyond the tropics, mostly in humid lowland subtropical climates, in highlands in southern Asia, and along the rim lands of the Mediterranean Sea. The northernmost native palm is ''Chamaerops humilis'', which reaches 44°N latitude along the coast of Liguria, Italy. In the southern hemisphere, the southernmost palm is the ''Rhopalostylis sapida'' (nīkau), which reaches 44°S on the Chatham Islands where an oceanic climate prevails. Cultivation of palms is possible north of subtropical climates, and some higher latitude locales such as Ireland, Scotland, England, and the Pacific Northwest feature a few palms in protected locations and microclimates. In the United States, there are at least 12 native palm species, mostly occurring in the states of the Deep South and Florida.

Palms inhabit a variety of ecosystems. More than two-thirds of palm species live in humid moist forests, where some species grow tall enough to form part of the canopy and shorter ones 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 , 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. A few palms are adapted to extremely basic lime soils, while others are similarly adapted to extreme potassium deficiency and toxicity of heavy metals in serpentine soils.

Taxonomy

Palms are a monophyletic group of plants, meaning 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 15 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 6 subfamilies. A few general traits of each subfamily are listed below.
* Subfamily are the largest subfamily with 14 tribes and 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.
* Subfamily 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 has small to medium-sized flowers, spirally arranged, with a gynoecium of three joined carpels.
* Subfamily are the second-largest subfamily with 8 tribes. Most palms in this subfamily have palmately lobed leaves and solitary flowers with three, or sometimes four carpels. The fruit normally develops from only one carpel.
* Subfamily contains only one species, ''Nypa fruticans'', which has large, pinnate leaves. The fruit is unusual in that it floats, and the stem is underground and dichotomously branched, also unusual in palms.

The is the sixth subfamily of Arecaceae in N.W. Uhl and J. Dransfield's 1987 classification. Members of this group have distinct monopodial flower clusters. Other distinct features include a gynoecium with five to 10 joined carpels, and flowers with more than three parts per whorl. Fruits are multiple-seeded and have multiple parts. From the modern phylogenomic data, the Phytelephantoideae are tribe in the Ceroxyloideae subfamily.

Currently, few extensive phylogenetic studies of the 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 the Calamoideae are monophyletic, and Ceroxyloideae and Coryphoideae are paraphyletic. The relationships of Arecoideae are uncertain, but they are possibly related to the Ceroxyloideae and Phytelephantoideae. Studies have suggested the lack of a fully resolved hypothesis for the relationships within the family is due to a variety of factors, including difficulties in selecting appropriate outgroups, homoplasy in morphological character states, slow rates of molecular evolution important for the use of standard DNA markers, and character polarization. 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.

Recently, nuclear genomes and transcriptomes have been used to reconstruct the phylogeny of palms. This has revealed, for example, that a whole-genome duplication event occurred early in the evolution of the Arecaceae lineage, that was not experienced by its sister clade, the Dasypogonaceae.

For a phylogenetic tree of the family, see the list of Arecaceae genera.

Selected genera

* ''Archontophoenix''— Bangalow palm
* ''Areca''— Betel palm
* ''Astrocaryum''
* '' Attalea''
* ''Bactris''— Pupunha
* ''Beccariophoenix''—Beccariophoenix alfredii
* ''Bismarckia''—Bismarck palm
* ''Borassus''—Palmyra palm, sugar palm, toddy palm
* ''Butia''
* ''Calamus''—Rattan palm
* ''Ceroxylon''
* '' Cocos''—Coconut
* ''Coccothrinax''
* ''Copernicia''—Carnauba wax palm
* ''Corypha''—Gebang palm, Buri palm or Talipot palm
* ''Elaeis''—Oil palm
* ''Euterpe''—Cabbage heart palm, açaí palm
* ''Hyphaene''—Doum palm