Palm: Microcoelum martianum

Palm leaves are large, stalked and furnished with a sheath at the base. In the juvenile stage the leaf is whole but during growth it breaks up into sections along the veins and thus in maturity it is either pinnate (cocos — coconut-palm) or fan-shaped (corypha – talipot-palm). Often it is palmate (washingtonia) or two-lobed (chamaedorea), and in rare instances bipinnate (caryota — fishtail-palm).

The inflorescence of a palm consists of a cluster of trimerous, usually unisexual flowers arranged in a spike (spadix) enclosed by a spathe, or several spathes. Most palms have axillary flowers, produced a number of times during the tree’s lifetime. Some species, however, have terminal flowers and these are then extremely large: in the genus Corypha it is estimated that a single cluster contains as many as 100,000 flowers. The genera Corypha, Metroxylon – sago-palms, and Caryota die after the flowers have faded and the seeds have ripened – a phenomenon known as hypaxanthy. Though inconspicuous, the flowers are very fragrant and secrete nectar, a fact well known to entomologists working in the tropics who never pass up the opportunity of examining such a flower which attracts scores of insects. Insects are also the chief pollinators of palm trees, other agents being the wind and in rare instances even humming-birds and other birds that catch insects on the flowers.

The fruits of palm trees are not nuts, as is commonly but mistakenly believed, but berries or drupes, called armoured berries when they are ripe and the outer covers have dried. The seeds have a well-developed endosperm, which is either hard and horny such as in the genus Phytelephas (sometimes classed as a separate family) and can be used as plant-ivory for carvings, or soft and oily. In the course of germination the ovary becomes elongated, with part of it remaining in the seed, and serves to carry food from the endosperm to the embryo which develops outside the seed. This form of nourishment from the endosperm may last for several years, as with the coconut.

Palms are typical plants of the tropics and sub-tropics, represented in Europe by the well-known Chamaerops humilis and C. macrocarpa from the Mediterranean region. In 1967 a third European palm, Phoenix theophrasti, the date palm, was discovered on Crete in the province of Sitia.

15. November 2011 by Dave Pinkney
Categories: Featured Articles | Comments Off on Palm: Microcoelum martianum

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