Dichotomy

Dichotomy [ Biology ]
Adjective: Dichotomous or Dichotomic
Adverb: Dichotomously
Noun: Dichotomousness

Dictionary of botanic terminology
index of names


	In a broad sense dichotomy is a split or division into two non-overlapping or mutually exclusive parts or classifications.

Dichotomy [ Botany ]

In botany a dichotomy is the successive division and subdivision, as of a stem or branch of a plant or a vein of the body, into two parts as it proceeds from its origin; a successive bifurcation.

Strombocactus disciformis forma dicotomica

The place where a stem or vein is forked.

For example (photo at left) a dichotomously branched specimen of Stombocactus disciformis.

See also: Polytomy

Dichotomy [ Taxonomy ]


	In taxonomy a dichotomy is a division or distribution of genera into two species a division into two subordinate parts.

Such dichotomies are used as part of the process of classifying species, to build a taxonomic key. When classifying, a series of questions is asked which narrows down what is being examined, to indicate where it belongs in the hierarchy.
An example of dichotomy is the question "does it have a glochids?", used to divide the cactus species into plants belonging to the Opuntioideae subfamily ( with glochids) and into other subfamily of Cactaceae (Glochid-less).

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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