Bifrenaria - Description

Description

Bifrenaria are generally robust plants, of sympodial growth, between ten and sixty centimeters tall. They are characterized by round-section root with thick velamen, four-angled fleshy pseudobulbs of one internode, often basally protected by dried sheaths and with only one apical leaf(except for Bifrenaria steyermarkii, which occasionally has two), plicate (fan-folded) enervated leathery leaves, yet malleable and not exceedingly thick, with a pseudo-petiole of basal round section, and a basal inflorescences bearing up to ten flowers, which seldom surpass the leaves' length.

Bifrenaria flowers are strongly scented, they have sepals slightly larger than the petals, with the lateral ones basally united to the column foot forming a calcar with truncated extremity.The column is slightly arching, generally without wings or any other appendages, bearing a foot which the labellum is hinged to, whose shape varies, articulated to the column, with a longitudinal channeled callus often with a basal claw. Flowers show two elongated stipes, hardy ever one, at least twice longer than wide, with salient viscidium, visible caudicles and retinacle in inverted positions. The superposed pollinia number four, and are protected by a deciduous incumbent anther. Fruits are green, erect or pendulous; they take about eight months to ripe and hold hundreds of thousand yellowish or brownish elongated seeds up to 0.35 mm long. Among all the mentioned, the main characteristic distinguishing Bifrenaria from its closest relatives is the presence of the calcar. Other important characters are the four-sided single-leaved pseudobulbs besides the raceme inflorescence with two to ten flowers.

Little is known about pollination in Bifrenaria. Apparently the only existing records report the presence of some large species' pollinia observed on the back of male Eufriesea violacea bees (Euglossinae), and of Bombus brasiliensis (Bombini). Although there are no reports of flower pollination being directly observed, a paper published in 2006 studied the micromorphology of the labellum in Bifrenaria species, looking for substances useful to insects as food. The absence of such substances on the densely pubescent surface of most Bifrenaria labelli seems to indicate possible pollination by large bees as the major mean. Another indicator of this possibility is the strong smell emanated by species like B. tetragona which are similar to those of plants in other families which are also pollinated by these bees. The smaller pubescent species may be pollinated by smaller bees, while the smooth ones, which have strong colored flowers, as B. aureofulva, might be pollinated by hummingbirds.