HORSETAIL (Equisetum), the sole genus of the botanical natural order Equisetaceae, consisting of a group of vascular cryptogamous plants (see Pteridophyta) remarkable for the vegetative structure which resembles in general appearance the genera of flowering plants Casuarina and Ephedra.
On the east coast the force of the north-east monsoon, which beats upon the shores of the China Sea annually from November to February, has kept the land for the most part free from mangroves, and the sands, broken here and there by rocky headlands thickly wooded, and fringed by casuarina trees, stretch for miles without interruption.
The liquidambar and nutmeg may be noticed among the former; the first is one of the most conspicuous trees in Java, on the mountains of the eastern part of which the casuarina, one of the characteristic forms of Australia, is also abundant.
The Australian Eucalyptus and Casuarina in great variety, and many other imported trees, including syringas, wattles, acacias, willows, pines, cypress, cork and oak all thrive when properly planted and protected from grass fires.
Amongst the most remarkable galls recently discovered we may mention those found on Eucalyptus, Casuarina and other trees and plants in Australia.
In the natural order Rosaceae, the series Querciflorae, and the very anomalous genus Casuarina and others, instead of a single macrospore a more or less extensive sporogenous tissue is formed, but only one cell proceeds to the formation of a functional female cell.
In Casuarina, Juglans and the order Corylaceae, the pollen-tube does not enter by means of the micropyle, but passing down the ovary wall and through the placenta, enters at the chalazal end of the ovule.
In places the sands are fringed by long lines of Casuarina trees; in others, and more especially in the neighbourhood of some of the river mouths, there are deep banks of black mud covered with mangroves; in others the coast presents to the sea bold headlands, cliffs, mostly of a reddish hue, sparsely clad with greenery, or rolling hills covered by a growth of rank grass.
Recent additions are the eucalyptus, casuarina, Pinus pinea and ailanthus.
The finer branches are green, and bear a close resemblance to the stems of Equisetum and to the slender twigs of Casuarina; the surface of the long internodes is marked by fine longitudinal ribs, and at the nodes are borne pairs of inconspicuous scale-leaves.