Palms, though capable of reaching tree-like dimensions, differ from typical broad-leaved trees in profound ways that affect aspects of their cultivation.

Palms belong to the division of the flowering plants known as the monocots. This group includes the lilies, grasses, irises, orchids and bromeliads. Most monocot families consist of primarily herbaceous plants, that is, low-growing, soft-tissued plants. Very few other species of monocots attain the size of many palms. This is largely due to certain constraints placed on the development of the stems and monocots which in turn distinguish them from the second division of flowering plants, called dicots.

All of our favorite flowering trees and shrubs, and most of our shade trees, are dicots. Oaks, maples, azaleas, roses and most garden annuals are dicots. Dicots have a developmental feature that virtually all monocots lack. Within the stems of woody dicots, the water and food conducting tissue occurs in complete, concentric rings. In monocots, these same vascular tissues occur in bundles scattered throughout the internal tissue of the stem, rather than in complete rings. In dicots, a specialized layer of cells called the vascular cambium is formed between the water conducting rings (xylem) and the food conducting rings (phloem). The vascular cambium produces new rings of xylem toward the inside of the stem, and new rings of phloem toward the outside. For the vast majority of monocots, including all palms, no vascular cambium exists. What is the consequence of having or not having a vascular cambium? Woody dicots, blessed by nature with a vascular cambium, are capable of what plant scientists call secondary growth. This means that a dicot tree stem is always producing new vascular tissue and increasing in diameter as it ages. The vascular cambium also allows a dicot tree to repair injuries to its stem fairly efficiently, and horticulturists to successfully graft stems or buds of one species or variety onto the stem of another closely related species. This ability to produce secondary growth is evident in the pattern of growth rings that can be seen in a cross-section of a woody dicot stem. Unlike an oak tree or an apple tree, palms are essentially incapable of secondary growth and do not produce annual growth rings. Once a palm stem achieves its maximum girth at a given point on the stem, it is largely incapable of increasing its stem diameter.

Furthermore, the bundles of conducting tissue within the palm stem must last the entire life of the palm. Once a palm stem achieves its maximum diameter, not one single additional vascular bundle will be added to the internal tissue of the stem! Palms are also not able to repair their vascular bundles if damage is received to the stem. And, not surprisingly, it is impossible to graft one part of a palm to another. Most importantly of all, the future of a palm stem rides upon the continued health of a single actively growing bud or `palm heart' with little or no ability to regenerate itself. Very few palms have the ability to branch on their aerial stems. Thus, if the palm heart is killed, the entire palm (if solitary) or the palm stem (if clustering) is doomed to eventual death. With this in mind, it becomes all the more remarkable that palms have been able to reach such scales of height as they are indeed capable. P. B. Tomlinson of Harvard University, who has studied the structural biology of palms in detail, likens their stems (fibrous, vascular bundles scattered in pithy stem tissue) to steel-reinforced concrete, a telling analogy indeed!

Unlike broad-leaved trees, palms complete their thickening growth or increase in diameter before elongating. This is most evident in those palms that do not develop a conspicuous aerial trunk for a number of years (Sabal spp., for example), but is true for all palm species. During this `establishment phase', as Tomlinson has called it, the palm is particularly sensitive to growth checks or less than optimal conditions.

Typical of all monocots, the functioning root system of a palm develops from the stem. Very shortly after seed germination, the seedling root of a palm ceases to function and is replaced by roots produced from a specialized area of the stem called the root initiation zone. It is during the establishment phase of its growth that a young palm fully develops this initiation zone at the base of the stem. Such roots, originating from the stem, are called adventitious, in contrast to the underground root system of dicots which develop sequentially from a perennial seedling root. Again, unlike dicots, palm roots emerge from the stem at maximum thickness; they are incapable of secondary growth. They can branch, however, to three levels.
The third rank of root branches are the thinnest and function primarily in absorption of water and nutrients. Palm roots do not produce root hairs. Palm roots are capable of significant lateral growth; roots of some palms have been measured well over a hundred feet from the parent trunk. On some palms the root initiation zone extends for some distance above ground level on the trunk. Most extreme in this regard are the `stilt-root' palms of tropical rain forests that produce long, thick support roots from as high as 6 to 10 feet above the trunk base. Extensions of the root initiation zone can also be seen on those date palm species that produce a mass of aerial root stubs at the trunk base.
A few palms (Chamaedorea spp.) form aerial roots all along their stems.

The stems or trunks of palms are as diverse as the palms themselves, varying in thickness, shape, surface features and habit.
Though none are treated in this book, a sizable group of palms even grow as high climbing vines into the canopies of rain forest trees. Many palm stems remain covered with the remains of old leaf bases for many years; others shed their dead leaves very readily.

Trunk of Paurotis Palm (Acoelorraphe wrightii)

For the first years of a palm’s life, the stem consists of little more than overlapping leaf bases shielding the all important bud or palm heart. Some palm trunks swell noticeably at the base as they develop with age; others develop conspicuous bulges further up on the stem. Most tall growing palms eventually produce a clear trunk, usually gray or brown, sometimes green. The trunks of some palms are conspicuously spiny; these spines are often the remains of fibers that occurred within the tissue of the leaf bases.
Trunk of Zombia antillarum (Zombie Palm)

The scars left behind by fallen leaves frequently create a distinctive pattern on the trunk. These may appear as rings, or, if the leaves incompletely sheath the trunk, variously shaped scars. The point on the stem at which a leaf scar occurs (or where a leaf is still attached) is called a node. Very few palms are capable of branching on their aerial stems in the normal course of their growth; occasionally an aberrant individual of an otherwise non-branching species will produce a branched head.
Trunk of Phoenix dactylifera (Date Palm)

Hastula on upper surface of fan palm leaf

The leaves of palms are the largest such organs in the plant kingdom. All palm leaves consist of three main parts: the blade, the petiole or leaf stem, and the leaf base. The leaf base is basically that part of the petiole that sheathes the stem. On many palms, the base remains attached to the trunk or stem for some time after the blade and the petiole drop off. In some cases, the pattern of leaf base stubs is a distinctive feature of the palm’s appearance.

The tubular leaf bases of some feather-leafed palms sheath each other so tightly around the stem that they form a conspicuous neck-like structure called a crownshaft. Often waxy and smooth, and sometimes attractively colored, the crownshaft is usually a structure of singular beauty. The leaf stem or petiole can be short or long; in a few species it is apparently obsolete. The petiole of a number of palm species is toothed along the margins, ferociously so in some. Palm leaf blades basically fall into three main classes, palmate or costapalmate (the fan palms), pinnate or bipinnate leaves (the feather palms), or entire leaves. The fan palms are classified as either palmate or costapalmate. Fan palm leaves are circular or shaped like an out-stretched hand. They are divided shallowly or deeply into a variable number of segments which are often split at the tips themselves. Palmate and costapalmate leaves are similar in appearance except for the extension of the leaf stem (petiole) into the blade of the costapalmate leaf. This extension is sometimes referred to as the costa. Costapalmate leaves are often twisted or folded sharply along or at the tip of the costa.
Pinnate Leaf (1) - Palmate Leaf (3) - Costapalmate Leaf (2)

Many fan palms have an additional feature called the hastula that is sometimes useful in identifying the species. The hastula is a small, thin, more-or-less rounded protuberance of tissue located at the point where the petiole meets the blade. Hastulas are most frequently located on the upper surface of the leaf; a few fan palms have them on both surfaces. It is blunt or pointed at the tip, and its function is unknown. Feather palm leaves consist of a network of individual leaflets arrayed along an extension of the leaf stem called the rachis. Pinnately compound palm leaves are feather leaves that are only once-compound; that is, there is only a single series of leaflets. The leaflets may be numerous or few, narrow or broad, pointed at the tip or blunt and toothed. They can be regularly arranged along the rachis or attached in groups of several.
Induplicate Leaflet (top) - Reduplicate Leaflet (bottom)

Bipinnately compound palm leaves are twice-compound; that is, the primary leaflets themselves consist of a system of smaller secondary leaflets. Bipinnately compound leaves are very rare in the palm family, occurring in only a single tribe (Caryoteae) of the subfamily Arecoideae. Entire-leafed palms have neither segments nor leaflets. Instead, the leaf consists of an unsplit (or at most two-lobed) blade, longer than it is wide. Of the palms treated in this book, only one species, Chamaedorea metallica, has an entire leaf. Interestingly, the first leaves of many palm seedlings are entire, regardless of what type of mature leaf occurs on the palm. Induplicate vs. Reduplicate Leaves. An important feature of palm leaves that has significance in the taxonomy and identification of the major groups within the family is the way in which the leaf segments (fan palms) or leaflets (feather palms) are folded around the main vein or midrib. Palms in which the leaflets or segments are folded upward, forming a `V’, are called induplicate. Palms in which the leaflets or segments are folded downward, forming an inverted `V’, are termed reduplicate. Most of the fan palms have induplicate leaves, while the majority of the feather palms have reduplicate leaves. The best place to look to determine which type of folding characterizes a particular species is right at the point where the leaflet attaches to the rachis (feather palms) or, on fan palms, the point where the segments first split from the rest of the leaf.

Bipinnate Leaf

Male Flowers of Senegal Palm (Phoenix reclinata)

The individual flowers of a palm are generally quite small and inconspicuous, but are usually borne in such numbers on the flower stalk or inflorescence that they collectively are showy. The inflorescences of palms are frequently quite long and much-branched, but on some species they are short and spike-like (unbranched).
Flower of Pinanga kuhlii (Ivory Cane Palm)

On palms with crownshafts, the flower stalks are usually produced from the trunk below the crownshaft, and thus below all the leaves as well. On palms without crownshafts, the inflorescences emerge from among the leaves. On a few palms whose stems flower once (Corypha spp. and Nannorrhops ritchiana), the flower stalks appear to originate at the tips of the stems. Some palm flower stalks are backed by a large, boat-like bract or spathe that may persist even in fruit. The parts of the simplest palm flowers occur in three’s or multiples thereof; however, there is an enormous amount of variation in flower structure throughout the family. Likewise, palms vary greatly in the gender allocation of their flowers. Some have bisexual flowers with both functional male and female reproductive organs.
Many palms have separate male and female flowers on the same plant, usually on the same inflorescence. Other palm species produce separate male and female plants altogether, with flowers of only one sex occurring on any one particular plant. All date palms (Phoenix spp.) fit in this third category. The small size and fairly bland coloration of most palm flowers first led botanists to conclude that most palms were pollinated by wind. It is now known that, in fact, most palms are insect pollinated.

Flowers of Clustering Fishtail Palm (Caryota mitis)

Fruits of King Alexander palm (Archotonphoenix alexandrae)

In contrast to the often diminutive flowers, the fruits (and seed as well) of many palms species are fairly large and conspicuous. In fact, the largest seed of any plant known on the face of the earth belongs to a palm, the double coconut (Lodoicea maldavica).
Fruits of Queen Palm (Syagrus romanzoffiana)

The majority of palm fruits are classified as drupes. A drupe is defined as a fleshy, one-seeded fruit that does not open or split at maturity. Some palm fruits qualify as berries. A number of palm fruits contain more than one seed, but the majority carry only one seed within. The fruits of most palms have a fleshy or fibrous outer wall that is frequently attractively colored. For more than a few species, the display afforded by the ripe fruits is much more conspicuous than that of the flowers! The seed within a palm fruit is protected by a bony or fibrous coat. The seed coat of some species bears interesting patterns of ornamentation or sculpturing on its surface.
Fruits of Livistona chinensis (Chinese Fan Palm)

Most of the volume of the seed is taken up by the nutritive tissue called endosperm that feeds the developing seedling. The actual embryo of a palm is quite small, and is located in a small chamber at one end of the seed.

Fruits of Christmas Palm (Adonidia merrillii)

The palm family, consisting of 2300 to 2700 species, is known to botanists as the Palmae or the Arecaceae. That branch of botany devoted to formulating the classification of plants is called taxonomy. Relative to many other large and economically important plant families, the Arecaceae has not been well studied taxonomically, largely due to the difficulty in preparing dried field specimens of palms, and the fact that well over 90% of the palm family’s diversity is found in the tropics. In 1987, a landmark occurred in the taxonomic history of the palm family with the publication of Genera Palmarum by Drs. Natalie Uhl of Cornell University’s Bailey Hortorium and John Dransfield of the Royal Botanic Gardens at Kew. Inspired by years of work at the Bailey Hortorium by the late Harold Moore, Genera Palmarum presented the first complete, modern system of classification for the palm family through the rank of genus (a group of related species believed to be of common ancestry and defined by certain important shared characteristics that sets them apart from other species groups). Uhl and Dransfield recognized 200 genera (the plural for genus) in the palm family. These genera are organized into six subfamilies defined by certain important characteristics shared by all the component genera.

The subfamilies in turn are subdivided into tribes.
These subfamilies and tribes are listed below.

Family Arecaceae or Palmae

Subfamily Arecoideae
Tribe Areceae:
(Archontophoenix, Areca, Carpentaria, Chrysalidocarpus, Cyrtostachys, Dictyosperma, Euterpe, Neodypsis, Pinanga, Ptychosperma, Roystonea, Veitchia, Wodyetia)
Tribe Caryoteae: (Arenga, Caryota) Tribe Cocoeae: (Acrocomia, Allagoptera, Bactris, Butia, Cocos, Elaeis, Heterospathe, Howea, Jubaea, Syagrus)
Tribe Geonomeae
Tribe Iriarteae
Tribe Podococceae

Subfamily Calamoideae
Tribe Calameae
Tribe Lepidocaryeae

Subfamily Ceroxyloideae
Tribe Cyclospatheae:
(Pseudophoenix)
Tribe Ceroxyleae:
(Ravenea)
Tribe Hyophorbeae: (Chamaedorea, Gaussia, Hyophorbe)

Subfamily Coryphoideae
Tribe Borasseae: (Bismarckia, Borassus, Hyphaene, Latania)
Tribe Corypheae: (Acoelorrhaphe, Brahea, Chamaerops, Coccothrinax, Copernicia, Corypha, Licuala, Livistona, Nannorrhops, Pritchardia, Rhapidophyllum, Rhapis, Sabal, Serenoa, Thrinax, Trachycarpus, Trithrinax, Washingtonia, Zombia)
Tribe Phoeniceae: (Phoenix)

Subfamily Nypoideae
Subfamily Phytelephantoideae

No horticulturist working in the tropics or subtropics can afford to be indifferent to the loss of biodiversity that is currently taking place throughout the world’s tropics, fueled in part by the desire of tropical, Third World countries to achieve the status of First World economies and deal with explosive population growth, but in equal measure caused by the developed nations’ insatiable appetite for world resources to support affluent and frequently wasteful lifestyles. Palms are first and foremost a tropical plant family, and the numerous species are known only from single populations or inhabit restricted ranges of distribution.

In the past, palms were sometimes spared from destruction because the fibrous trunks would very quickly dull the blades of axes, but in these days of chainsaws and wholesale forest burning, rain forest palms are as easily reduced to ash and charred stumps as any other tree.

While horticulture can help in the preservation of many rare palms that might otherwise disappear off the face of the earth, conservation of palms in their intact habitats also preserves their unique relationships to their natural environment, from the insects that pollinate their flowers, to the animals that eat their fruit. A number of palm species are now represented in cultivation by more individuals than ever existed in the wild. Nonetheless, over-zealous collection of seeds or plants from the wild can also place pressure on rare palms.

Within the world of palm horticulture, horror stories circulate about rare palms being cut down in order that their seed crop could be collected and sold. Palm horticulturists need to become more sensitive to the source of the palms in commerce. Do not purchase rare palms that have been collected from the wild, unless you know for a fact that their habitat was slated for destruction or development.

The International Palm Society is a not-for-profit organization devoted to the support of palm research, education, conservation and cultivation. The Society has a number of local chapters in the United States and abroad, publishes a high quality and informative quarterly journal called "Palms", (formerly "Principes"), manages a seed fund for members from which seed of many rare palms can be purchased for nominal cost and holds a biennial meeting in various locations around the world that draws members internationally.
For membership information write to:
International Palm Society
P.O. Box 1897
Lawrence, KS 66044, USA.