Arecoideae

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 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. 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. Many 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").

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. These aberrations suggest the habit operates on a single gene.

Palms 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 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'', 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 deep southeastern states 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

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