Dating origin orchidaceae
Epiphytic orchids, those that grow upon a support, have modified aerial roots that can sometimes be a few meters long.In the older parts of the roots, a modified spongy epidermis, called a velamen, has the function of absorbing humidity.The base of the stem of sympodial epiphytes, or in some species essentially the entire stem, may be thickened to form a pseudobulb that contains nutrients and water for drier periods.The pseudobulb has a smooth surface with lengthwise grooves, and can have different shapes, often conical or oblong.The cordate leaves of Psychopsis limminghei are light brownish-green with maroon-puce markings, created by flower pigments.
Orchids are easily distinguished from other plants, as they share some very evident, shared derived characteristics, or synapomorphies.One is used as a food reserve for wintry periods, and provides for the development of the other one, from which visible growth develops.In warm and constantly humid climates, many terrestrial orchids do not need pseudobulbs.The root caps of terrestrial orchids are smooth and white.
Some sympodial terrestrial orchids, such as Orchis and Ophrys, have two subterranean tuberous roots.
The Orchidaceae have about 28,000 currently accepted species, distributed in about 763 genera.