Mesadenus
Mesadenus is a genus of the orchid family ( Orchidaceae). It contains seven species that are native to tropical America.
Description
The Mesadenus species are herbaceous plants. The roots arise in bunches, they are fleshy, spindle- shaped and hairy. The leaves are in a basal rosette, flowering time, they are already wilted. The leaves are petiolate, the petiole includes the shoot, he is shorter than the leaf blade. The leaf blade is ovate to lanceolate vice versa. The leaf surface is shiny green, sometimes covered by a network of different colored leaf veins.
The terminal, einseitswendige, racemose inflorescence is hairy at the top. Some bracts, which become smaller upward, wrap it in part. The numerous fragrant flowers are small, their color is green or reddish brown. The glabrous bracts have the same color as the flowers. The ovary is sessile, oblique spindle -shaped and has obliquely upward. Sepals which are each formed almost the same, they are roughly parallel to each other to form a tube, only the tips are curved slightly outwardly. The dorsal sepal is slightly concave and fused for a short distance to the column. The lateral sepals are fused together at the base for a short distance and set with slate base of the pedestal, where they form a small depression for the nectar. The petals are the dorsal sepal and stick with their inner edges there on, their tops are free. The lip is sitting, in some species at the base with two rear facing nectar glands. The leaf surface of the lip is rinnig, the sides are bent up and adhere to the column. The column is club-shaped, at the base of them joint with the ovary reaching out ( pedestal ). The scar is semicircular to bilobed and U-shaped. The stamen is deeply cordate at the base, in front with retracted tip or rounded. It contains the elongated, loosely stuck together pollinia attached to a common, centrally seated viscid disc ( Viscidium ) depend. The separation layers between stamen and stigma ( rostellum ) is just a flat diaphragm with a small central peak. The capsule fruit is obovate and slightly asymmetrical.
Occurrence
Mesadenus comes in tropical America into two disjoint sub-regions before: Once in Central America, Mexico, Florida and the Caribbean, the second in southeastern Brazil. The species grow on relatively dry sites in grassland, savanna and open woodland. They come right up to altitudes of 2850 meters.
Systematics and botanical history
Mesadenus is classified within the tribe Cranichideae in the subtribe Spiranthinae. The genus was described in 1920 by Rudolf Schlechter. The name comes from the Greek words meso μέσος, "middle", and ἀδένος adenos, " gland ", together. It refers to the center fitting to the pollinia Viscidium. Lectotype is Mesadenus galeottianus, a synonym of Mesadenus polyanthus.
The genus Mesadenus is closely related to some species of the genus Schiedeella. Balogh 1982 Mesadenus looked at only as a section of a broad genus Brachystele.
The following species are included in genus Mesadenus:
- Mesadenus affinis ( C.Schweinf. ) Garay
- Mesadenus chiangii ( M.C.Johnst. ) Garay
- Mesadenus glaziovii ( Cogn. ) Schltr.
- Mesadenus lucayanus ( Britton ) Schltr.
- Mesadenus polyanthus ( Rchb.f. ) Schltr.
- Mesadenus rhombiglossus ( Pabst ) Garay
- Mesadenus tenuissimus ( L.O.Williams ) Garay