Morphological and Ecological Diversity of Palms

Scott Zona, Ph.D., Palm Biologist

Palm Facts

• Family Palmae or Arecaceae of the Arecales.
• 191 genera and 2500 species.
• Ancient lineage. Macrofossils of palms are known from the upper Cretaceous (fossilized stems and leaves); Nypa pollen known from the upper Cretaceous.
• Distributed from southern Oklahoma to central Chile, from southern France to South Africa, from southern Japan to New Zealand.
• Most diverse in NW South America and SE Asia. Found in rain forest, seasonal forest, cloud forest, swamp, mangroves, gallery, savannah, desert. Some dominated by palms.
• Palms are keystone species-important food sources for vertebrates and insects. Oil palm and coconut palm are two of the world's top-ten agronomic crops.
• Record-holders: Palms are the tallest monocots (Ceroxylon: 60 m tall!), longest stems (a rattan at 175 m!), have the largest inflorescences (Corypha), the longest leaves (Raphia regalis, 25.11 m!), the largest seeds (Lodoicea) in the Plant Kingdom.

Architectural Diversity:

Architecture models (based on Hallé & Oldeman 1970) based on three main criteria:

1. presence and kind (dichotomous or not) of aerial branching,
2. the presence basal branching,
3. terminal or axillary inflorescences (hapaxanthic [shoot dies after flowering] vs. pleoxanthic [shoot lives and flowers again and again]).

These models are inconsistent and not perfect, but they are the only ones available.

• Corner's Model: Palms of this model have single terminal bud and axillary inflorescences, pleoxanthic or hapaxanthic. Cocos, Roystonea, Metroxylon amicarum (pleoxanthy); Caryota urens (hapaxanthic).
• Tomlinson's Model: Basal branching (= suckering = multiple stems), pleoxanthic or hapaxanthic. Chamaedorea sefreitzii, Ptycho. macarthurii--pleoxanthic; or Metroxylon sagu--hapaxanthic (stems have single terminal bud)
• Holttum's Model: Single, unbranched stem and a terminal inflorescence (hapaxanthic) Corypha, Metroxylon warbugii.
• Schoute's Model: Multiple terminal buds via dichotomous branching: Nypa fruticans, non-suckering Hyphaene.

Odd-balls:

• Serenoa: axillary branches (non-dichot) and axillary pleoxanthy (Attims' Model)
• Nannorhops ritchiana: suckering, aerial dichotomies, one of which becomes hapaxanthic
• Hyphaene suckering spp.: basal branching (suckering) is non-dichot; aerial branching is dichotomous.

Variations in Habit:

Tree palms--Cocos (emergent); Geonoma (understory). Large tree palms common in savannahs, disturbed areas, gaps, gallery forest, beaches, and open forest.

Shrub palms--Chamaedorea, Calyptrogyne. Most understory palms are small, clustering, with undivided lvs. Creeping, rhizomatous palms are common in rapidly changing areas, such as flood zones, where they form dense, clonal thickets (e.g. Bactris major).

"Acaulescent" palms--Sabal etonia, Syagrus petraea. Fire adapted.

Lianas--climbing with non-selfsupporting stems. Independently evolved in four subfamilies. Parallel evolution.

Suckering as in Calamus and Desmoncus or solitary in Calamus and Calospatha. Lianas arose in at least four lineages: Calamoid, Dypsis, Chamaedorea, Desmoncus. Adaptations for climbing. Cirrus is modified leaf tip. Flagellum is modified inflorescence.

Unusual Life forms

Litter-trappers--Entire leaves held in erect to funnel litter to center of crown. Absorption is probably from throughfall of precipitation, rather than directly through leaf cuticle. --Asterogyne martiana, Marojejya, Masoala

Mangrove--growing in brackish or salt water. Example: Nypa, dichot branching in mud. Phoenix paludosa in India; Raphia taedigera in swamps of Central America not mangroves

Rheophytes--growing in flood zone of rivers. Low bushy, flexible stems, narrow willow-like leaf segments. Examples: Ravenea musicalis: viviparous, fruit floats but seedling sinks, first cataphylls are recurved and hook-like, leaves sway in water. Other examples: Chamaedorea cataractarum. Pinanga rivularis- has fruits with spreading hooked mesocarp fibers that catch in the rocks of river.

Bottle & Belly palms--fusiform or ventricose or lageniform stem.

Stems with water storage. Common on islands. Examples: Roystonea regia, Gastrococos, Gaussia princeps, Colpothrinax, Copernicia ; Iriartea ventricosa; Hyophorbe lagenicaulis (Bottle palm). Some palms simply have uniformly massive water-storing stems. Sabal causiarum of Hispaniola and Puerto Rico, Copernicia fallaense of Cuba, and Jubaea chilensis of Chile are three familiar examples.

Leaf diversity:

Largest leaves over 25 m long. Smallest palm leaf is only about 15 cm long. Leaves have both raphides (calcium oxalate) and silica bodies, an unusual combination. Leaves may be divided or undivided.

3 major kinds of leaves palmate, pinnate, costapalmate divided (not compound, as in legumes). Bipinnate in one palm, Caryota.

All palm leaves are plicate, i.e. have accordion folds, which are formed by differential growth of surface of leaf initial. Segmentation is then superimposed on the accordion folds of the leaf. Segments plication usually divided into two kinds: reduplicate (edges folded down) and induplicate (edges folded up-- holds water "in"). However, departures from these two options do exist.

Floral Diversity

Flowers of palms are usually trimerous, with three imbricate sepals, three imbricate petals, six stamens in two whorls, and three free uniovulate capels that are superior. Inflorencesces are usually paniculate. Exceptions include tetramery in Phytelaphantoideae and Chelyocarpus p. p. and dimery in Chelyocarpus p. p. Connation and adnation of parts are very common. Valvate petals are found in many genera. Various groups have increased stamen number (Ptychospermatoideae, Caryoteae, Oncospermatinae, Phytelephantoideae, and many others). Pollen morphology is variable, although some entire subfamilies or tribes have uniform pollen. Noteworthy for their variable pollen are the Calamoideae, Borasseae, and Pinanga. The gynoecium of palms may be apocarpus or syncarpus. In the Arecoideae, the gynoecium is usually pseudomonomerous: the syncarpus tricarpellate gynoecium is uniovulate by the abortion of two ovules. Other groups have more than three ovules: Attalea and Phytelephantoideae

Fruits and Seeds

Fruits may be dry or fleshy. A very few have have dehiscent pericarp (Astrocaryum, Schippia). Most are animal dispersed (see: "Additions to 'A review of animal-mediated seed dispersal of palms'"). Lodoicea maldivica has largest seed in the plant kingdom. Endosperm stores lipids, proteins, or mannans, but never starch.

Last modified: Updated 2005-08-11