Parapatric

Parapatric [ Botany - Biology ]	Dictionary of botanic terminology - index of names
Noun: Parapatrisim. Adverb: Parapatrically.

Pertaining to the ranges of species or populations that are contiguous but not overlapping.

(of biological species or speciation) Describing formation of two or more different species or populations that inhabit contiguous geographical areas (not overlapping or marginally overlapping) with the potential for gene flow between populations.
	In parapatric speciation, the new species evolve from contiguous populations, but nonetheless, the population does not mate randomly. Suppose now that a population initially existed in an area to which it was well adapted, and that it then started to expand into a contiguous area in which the environment favoured a different form. If the transition between the two environments was sudden, a stepped cline will evolve at the border, the border would be recognized as a hybrid zone. As selection worked on the population in the new area, different genes would accumulate in it and the two populations would diverge to become adapted to their respective environments. If they diverged almost to be different species the two populations would have separated while they were geographically contiguous, along an environmental gradient.
In contrast to the allopatric theory of speciation, the two populations on either side of the hybrid zone have diverged without any period of geographic separation. (compare: Sympatric, Allopatric)

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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