Central spines

Central spines [ Botany ]

Dictionary of botanic terminology - index of names


	Central spines (In Cactaceae family) are the usually longer and stronger spines arising from the centre of the areole, varying in number from one to several and clearly differentiated from radials.

Central spines (red) of Sclerocactus polyancistrus

All spines of cacti are located on an areole usually in a cluster at the tips of the tubercles.

The spines themselves, with often neatly organized arrangements, are identified as two groups: The central spines and the radial spines, of varying quantities and shapes.

Spines may differ considerably in immature and adult specimens of the same species. The spines can be long or short, numerous or inexistent.

An areole may bear also bristles, glochids and wool.

Central spines (if present) are the larger of the two types (stick out above the radials) and usually arise from the centre of the areole, varying in number from one to several, with or without a dominant(s) longer, stronger central spine, and secondary centrals of different shape, size and colour.
Centrals are also frequently differentiated in upper (adaxial), and lower (Abaxial) depending on they orientation. They are often of a different colour than the radials .
Radial spines are usually smaller and are located around the margin of the areole in a single or superimposed series of whorls .

Advertising

Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994