Arecaceae

Arecaceae
Temporal range: 80–0 Ma

Late Cretaceous- Recent

Coconut palm tree Cocos nucifera in Martinique.
Scientific classification
Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Arecales
Family: Arecaceae
Bercht. & J.Presl, nom. cons.[1]
Type genus
Areca
Subfamilies
Diversity
Well over 2600 species in some 202 genera

The Arecaceae are a botanical family of perennial climbers, shrubs, acaules and trees commonly known as palm trees (owing to historical usage, the family is alternatively called Palmae).[3] They are flowering plants, a family in the monocot order Arecales. Currently 181 genera with around 2600 species are known,[4] most of them 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, and palms are also widely used in landscaping, making them one of the most economically important plants. In many historical cultures, palms were symbols for such ideas as victory, peace, and fertility. For inhabitants of cooler climates today, palms symbolize the tropics and vacations.[5]

Morphology

Various Arecaceae
This grove of the native species Washingtonia filifera in Palm Canyon, California is growing alongside a stream running through the desert.

Whether as shrubs, trees, 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.[6]

Sawn palm tree trunk: Palms do not form annual tree rings.

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.[7] 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)[8] but some genera (e.g. Salacca) may contain two or more seeds in each fruit.

Coconut palm trees in Boracay, the Philippines
Palmyra palm fruit at Guntur, India

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.[9] This explains the cylindrical shape of the trunk (almost constant diameter) that is often seen in palms, unlike in true 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".[10]

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 60 m tall.[11] The coco de mer (Lodoicea maldivica) has the largest seeds of any plant, 40–50 cm in diameter and weighing 15–30 kg each. Raffia palms (Raphia spp.) have the largest leaves of any plant, up to 25 m long and 3 m wide. The Corypha species have the largest inflorescence of any plant, up to 7.5 m tall and containing millions of small flowers. Calamus stems can reach 200 m in length.

Range and habitat

Coconut palm trees in Mumbai, India

Most palms are native to tropical and subtropical climates. Palms thrive in moist and hot climates, however, they can be found in many 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 northwest 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 in along the coast of southern France.[12] In the southern hemisphere, the southernmost palm is the Rhopalostylis sapida, which reaches 44°S on the Chatham Islands where an oceanic climate prevails.[12] Cultivation of palms is possible north of subtropical climates, and some higher latitude locals such as Ireland, Scotland, England, and the Pacific Northwest feature a few palms in protected locations.

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.[13] 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 m, 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 extreme potassium deficiency and toxicity of heavy metals in serpentine soils.[12]

Two Roystonea regia specimens in Kolkata, India, note the characteristic crownshaft and apex shoot or 'spear'

Palms are a monophyletic group of plants, meaning the group consists of a common ancestor and all its descendants.[13] 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 six subfamilies.[14]

A few general traits of each subfamily are listed below.

The Coryphoideae are the most diverse subfamily, and are a paraphyletic group, meaning 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, or 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 species, Nypa fruticans,[15] 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, spirally arranged, with a gynoecium of three joined carpels.

The Arecoideae are the largest subfamily, with six diverse tribes (Areceae, Caryoteae, Cocoeae, Geonomeae, Iriarteeae, and Podococceae) 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.

The Phytelephantoideae are a monoecious subfamily. 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.[16]

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.[17] 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.[16]

Selected genera

See list of Arecaceae genera arranged by taxonomic groups or by alphabetical order for a complete listing of genera.

Silhouette of palm trees in Kwa-Zulu Natal, South Africa
Palm trees in Multan, Pakistan
Cuban Royal palm

Evolution

The Arecaceae are the first modern family of monocots appearing in the fossil record around 80 million years ago (Mya), during the late Cretaceous period. The first modern species, such as Nypa fruticans and Acrocomia aculeata, appeared 94 Mya, confirmed by fossil Nypa pollen dated to 94 Mya. Palms appear to have undergone an early period of adaptive radiation. By 60 Mya, 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.[18] Several species of palms have been identified from flowers preserved in amber, including Palaeoraphe dominicana and Roystonea palaea.[19] Evidence can also be found in samples of petrified palmwood.

Uses

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.[20] Date wood, pits for storing dates, and other remains of the date palm have been found in Mesopotamian sites.[21] 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.[20]

An indication of the importance of palms in ancient times is that they are mentioned more than 30 times in the Bible,[22] and at least 22 times in the Quran.[23]

Fruit of the date palm Phoenix dactylifera

Arecaceae have great economic importance, including coconut products, oils, dates, palm syrup, ivory nuts, carnauba wax, rattan cane, raffia, and palm wood.

Along with dates mentioned above, members of the palm family with human uses are numerous.

Sabal palm tree in the Canaveral National Seashore
Coconut flowers

Endangered species

Pritchardia affinis, a critically endangered species endemic to the Hawaiian Islands

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 those with small habitat ranges 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 palm's apical meristem, a vital part of the palm that cannot be regrown (except in domesticated varieties, e.g. of peach palm).[25] 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.[26] 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.[13]

However, several factors make palm conservation more difficult. Palms live in almost every type of warm habitat and have tremendous morphological diversity. Most palm seeds lose viability quickly, and 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 or truly imitate the natural setting.[27] Also, the risk of cross-pollination can lead to hybrid species.

The Palm Specialist Group of the World Conservation Union (IUCN) began in 1984, and has performed a series of three studies to find basic information on the status of palms in the wild, use of wild palms, and palms under cultivation. Two projects on palm conservation and use supported by the World Wildlife Fund took place from 1985 to 1990 and 1986–1991, in the American tropics and southeast Asia, respectively. Both studies produced copious 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.[27]

The rarest palm known is Hyophorbe amaricaulis. The only living individual remains at the Botanic Gardens of Curepipe in Mauritius.

Arthropod pests

Pests that attack a variety of species of palm trees include:

Symbolism

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. 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.

Panaiveriyamman was an ancient Tamil tree deity related to fertility. Named after panai, the Tamil name for the Palmyra palm, she was also known as Taalavaasini, a name that further related her to all types of palms.[32]

Today, the palm, especially the coconut palm, remains a symbol of the tropical island paradise.[13] Palms appear on the flags and seals of several places where they are native, including those of Haiti, Guam, Saudi Arabia, Florida, and South Carolina.

Other plants

Some species commonly called palms, though they are not true palms, include:

See also

References

  1. Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x, retrieved 2010-12-10
  2. "Arecaceae Bercht. & J. Presl, nom. cons.". Germplasm Resources Information Network. United States Department of Agriculture. 2007-04-13. Retrieved 2009-07-18.
  3. The name "Palmaceae" is not accepted because the name Arecaceae (and its acceptable alternative Palmae, ICBN Art. 18.5) are conserved over other names for the palm family.
  4. Christenhusz, M. J. M. & Byng, J. W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. Magnolia Press. 261 (3): 201–217. doi:10.11646/phytotaxa.261.3.1.
  5. Landscaping with Palms in the Mediterranean Archived June 21, 2006, at the Wayback Machine.
  6. Uhl, Natalie W. and Dransfield, John (1987) Genera Palmarum – A classification of palms based on the work of Harold E. Moore. Lawrence, Kansas: Allen Press. ISBN 0-935868-30-5 / ISBN 978-0-935868-30-2
  7. Arecaceae – University of Hawaii Botany
  8. Arecaceae in Flora of North America
  9. Chase, Mark W. (2004). "Monocot relationships: an overview". American Journal of Botany. 91 (10): 1645–1655. PMID 21652314. doi:10.3732/ajb.91.10.1645.
  10. Donoghue, Michael J. (2005). "Key innovations, convergence, and success: macroevolutionary lessons from plant phylogeny" (PDF). Paleobiology. 31: 77–93. doi:10.1666/0094-8373(2005)031[0077:KICASM]2.0.CO;2.
  11. :: Presidencia de la República de Colombia ::
  12. 1 2 3 4 Tropical Palms by Food and Agriculture Organization Archived May 6, 2006, at the Wayback Machine.
  13. 1 2 3 4 Virtual Palm Encyclopedia – Introduction
  14. N. W. Uhl, J. Dransfield (1987). Genera palmarum: a classification of palms based on the work of Harold E. Moore, Jr. (Allen Press, Lawrence, Kansas).
  15. John Leslie Dowe. Australian Palms: Biogeography, Ecology and Systematics. p. 83. Retrieved April 20, 2012.
  16. 1 2 Palms on the University of Arizona Campus Archived June 21, 2006, at the Wayback Machine.
  17. Hahn, W.J. (2002). A Molecular Phylogenetic Study of the Palmae (Arecaceae) Based on atpB, rbcL, and 18S nrDNA Sequences (Systematic Botany 51(1): 92–112).
  18. Virtual Palm Encyclopedia – Evolution and the fossil record
  19. Poinar, G. (2002). "Fossil palm flowers in Dominican and Baltic amber". Botanical Journal of the Linnean Society. 139 (4): 361–367. doi:10.1046/j.1095-8339.2002.00052.x.
  20. 1 2 W.H. Barreveld. "Date Palm Products – Introduction". Food and Agriculture Organization of the United Nations. Archived from the original on 19 June 2007. Retrieved 2007-06-12.
  21. Date Sex @ University of Pennsylvania Museum of Archaeology and Anthropology
  22. Bible search for "palm"
  23. Koran search for "palm"
  24. Revolutionary War Exhibit Text – November 2002 Archived November 10, 2006, at the Wayback Machine.
  25. Rose Kahele (August–September 2007). "Big Island Hearts". Hana Hou! Vol. 10, No. 4. Retrieved 2016-08-14.
  26. Dennis Johnson, ed. (1996). Palms: Their Conservation and Sustained Utilization (PDF). International Union for Conservation of Nature. ISBN 2-8317-0352-2.
  27. 1 2 Palm Conservation: Its Atecedents, Status, and Needs
  28. "Pest Alerts - Red palm mite, DPI - FDACS". Doacs.state.fl.us. Retrieved 2010-07-30.
  29. Robert E. Woodruff (1968). "The palm seed "weevil," Caryobruchus gleditsiae (L.) in Florida (Coleoptera: Bruchidae)" (PDF). Entomology Circular. Florida Department of Agriculture. 73: 1–2. Archived from the original (PDF) on 2011-07-24.
  30. Rhynchophorus ferrugineus at North American Plant Protection Organization (NAPPO)
  31. Ferry & Gómez. 2002. The red palm weevil in the Mediterranean. Vol. 46, No 4, Palms (formerly Principes), Journal of the International Palm Society. link http://www.palms.org/palmsjournal/2002/redweevil.htm link
  32. Symbolism of trees
  33. 1 2 3 4 5 6 7 8 9 (c) FAO 1995. Tropical Palms.. Introduction. http://www.fao.org/docrep/X0451E/X0451e03.htm NON-WOOD FOREST PRODUCTS 10. FAO – Food and Agriculture Organization of the United Nations. ISBN 92-5-104213-6
  • C. H. Schultz-Schultzenstein (1832). Natürliches System des Pflanzenreichs..., 317. Berlin, Germany.
  • Dransfield J., Uhl N.W., Asmussen C.B., Baker W.J., Harley M.M., Lewis C.E. (2005). "A new phylogenetic classification of the palm family, Arecaceae". Kew Bulletin 60: 559–569. [latest Arecaceae or Palmae classification]
  • Hahn, W.J. 2002. A Molecular Phylogenetic Study of the Palmae (Arecaceae) Based on atpB, rbcL, and 18S nrDNA Sequences. Systematic Botany 51(1): 92–112.
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