Hymen

Hymen [ Botany ]	Dictionary of botanic terminology - index of names
Synonyms: Annulus, Throat circle.

The “hymen” or “*annulus” is a narrow colored ring that circles the
inner wall of the distal throat found in the flowers of many Echinopsis, s.l. (including subg. Lobivia, Pseudolobia and Trychocereus), and serve as a nectar guide.

The throat circle or annulus colour often differs from and contrasts to the portion of the distal throat below it and to the colour of the flower petals situated adjacent to the circle. The throat-circle apparently serves as an attractant for day-flying pollinators to an opened flower and/or to orient a pollinator, already on a blossom, to the throat itself. The throat-circle is often set upon a slight bulge of the throat wall that circles the tip of the distal throat division.
The white contrasting "throat circle" in a flower of Lobivia backebergii	The black "throat circle" in a flower of Lobivia jajoiana
The annulus is variably developed in Echinopsis, s.l., but is most prominent in lobivias. It apparently functions to make the throat-circle more evident to a pollinator. In some cases, though, an annulus is greatly reduced or apparently absent. In some species (e.g. Lobivia jajoiana ) the throat-circle, is covered by a thin, stiff, transparent layer which is highly reflective. An insect looking down at a flower would see a gorgeous, iridescent terminals that flashed on and off as the flower fluttered in the breezes. This apparently is a great signal to attract pollinators.

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