Introduction to Palms
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Introduction to Palms
There are about 200 genera of palms with almost 3000 species, the majority of them confined to the tropical moist regions of the world, primarily between latitudes 20 deg N and 20 deg S and to areas having 500 mm (20 inches) or more of rainfall per year. The northernmost palm is Chamaerops humilis which grows around the Mediterranean in Europe and North Africa; the southernmost is Rhopalostylis sapida of New Zealand.
Some genera cover an extensive range beyond the tropics, for example Sabal,Syagrus and Livistona however most are more restricted in their range. Some to the extent that they occur only on specific islands and are not found elsewhere; for example, Juania, Hedyscepe, Hyophorbe and Brahea
Palms belong to a botanic order known as PRINCIPES, or the princes of the plant world, in which its single family is known as ARECACEAE (or PALMAE). This family is divided into six subfamilies further into 14 tribes and 36 subtribes and finally into around 200 genera - (Dransfield and Uhl 1986).
A genus is a group of species (or a single species) that closely resembles one another in flowers, fruit and vegetative characteristics. A genus bears a name in a similar way that a person is known by a surname and this generic name is taken to be the earliest published valid name for that group of palms (or palm). It may have had its origin in a particular characteristic of the palm, or was taken from the name of the discoverer. Many palms and other plants were named to honour a notable person of the time in the era when they were discovered.
An individual species in a genus is identified by a name similar to the first name of a person so that each species is known by a surname and a first name for example Howea forsteriana, or Phoenix canariensis. The surname (genus) is stated first and that of the name of the individual species follows.
Palms form a distinctive family in which most of them are easily identified by their form which is rarely confused with other families.
Although palms are a complex group of plants, they do have the same basic form. Their stems or trunks can be solitary or clustering. Palm stems can be tall or low to the ground; some have underground stems and others, slender climbing stems only a few millimetres in diameter. Some trunks are tall and cylindrical while others are swollen at the base or in the middle, being bottle shaped or spindle-like in appearance. Some palms retain the scars of their old leaves in the form of rings or nodes on the stem, or as old leaf bases still adhering to the trunk.
However palms do not have bark as do most other trees. Palm stems do not develop true wood with annual rings that are common to many trees - they often have hard stems that contain bundles of conducting vessels scattered throughout softer tissue. This structure gives the palm strength with flexibility; able to bend in strong winds.
The root systems of palms are usually numerous and generally do not branch like other plants. As a palm gets older, it produces new roots from the base of the stem and occasionally they may develop above ground level and form stilt or prop roots.
Many undergrowth and rainforest palms produce most of their roots near the surface of the soil and the roots grow beneath the humus across the forest floor. Palms naturally occurring in open forest or in seasonal rainfall areas send most of their roots downwards to anchor the palm, or in search of moisture.
The crown of leaves is the most distinctive feature of the palm and some palms have leaves that are the largest in the entire plant kingdom, for example
Leaves are one of two types: PALMATE, that is fan-shaped, or PINNATE, often referred to as feather-shaped leaves. In only one genus of palms,
Caryota, the pinnate leaves are further divided. These leaves are referred to as BIPINNATE. The leaflets are wedge-shaped segments that resemble the tail of a fish.
Within both of the leaf types there is a great diversity in size, shape and amount of division of the leaf into segments. This in unmatched in any other plant family. Palmate leaves can be large or small, entirely without a segment, as in the case of the tropical palm Licuala grandis, or divided with distinct segments, as in Rhapis excelsa. Intermediate forms also occur and such examples can be seen in
Livistona and Pritchardia
In some palmate leaves, the petiole does not terminate at a place on the base of the blade, but enters it so that the leaf appears to be intermediate between palmate and pinnate. Such leaves are referred to as COSTAPALMATE and some Sabal species are an example of this.
Pinnate leaves are commonly divided into leaflets, with each positioned along the leaf stem or rachis. Such leaflets can be narrow or broad, linear or wedge shaped. In some species for example Chamaedorea ernesti-augusti, the pinnate leaves are not divided but are entire. In others that are divided, the leaflets can be regularly arranged as in Howea forsteriana or irregularly arranged, for example Syagrus romanzoffiana. The latter has leaflets grouped in different planes to give the leaf a plumose appearance.
The colour of mature palm leaves can vary from deep green to pale green and from pale blue to silver or burgundy. Emerging leaves may also show colour ranging from deep-red (Chambeyronia macrocarpa) to bronze for some populations of Archontophoenix. As the leaf develops, the colour of an emergent leaf changes to that of the older leaves.
When palms flower, they usually produce an inflorescence with small insignificant flowers. The inflorescences are produced from within or below or even above the crown of leaves and for some species on lower parts of the trunk Palm flowers can be either unisexual or bisexual and the arrangement of palm flowers can be of three basic sexual forms;
MONOECIOUS - where male and female flowers are present on the same inflorescence or on separate inflorescences but on the same plant
DIOECIOUS - where male flowers and female flowers are on individual inflorescences and on separate plants.
POLYGAMOUS - where bisexual and unisexual flowers are combined in various ways on the same inflorescence. If unisexual flowers are absent, the arrangement is HERMAPHRODITE and the plant has only bisexual flowers.
After pollination, fruits are formed which usually contain only one seed. The seeds are usually ovoid (egg shaped), ellipsoid (solid ellipse), or globose (almost spherical) in shape and occur in a wide range of sizes from a few millimetres, as in Washingtonia robusta to almost half a metre in diameter as is the case with the 'Double Coconut', Lodoicea maldivica from the Seychelles Islands.
Palms & Cycads Beyond the Tropics, Keith Boyer.