Mesadenus

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Mesadenus
Systematics
Order : Asparagales (Asparagales)
Family : Orchids (orchidaceae)
Subfamily : Orchidoideae
Tribe : Cranichideae
Sub tribus : Spiranthinae
Genre : Mesadenus
Scientific name
Mesadenus
Schltr.

Mesadenus is a genus from the family of the orchid (Orchidaceae). It contains six species that are native to tropical America.

description

The Mesadenus species are herbaceous plants. The roots arise in clusters, they are fleshy, spindle-shaped and hairy. The leaves are in a basal rosette, by the time they bloom they are already withered. The leaves are stalked, the petiole includes the shoot, it is shorter than the leaf blade. The leaf blade is oval to inverted-lanceolate. The leaf surface is shiny green, sometimes covered by a network of differently colored leaf veins.

The terminal, one-sided, racemose inflorescence is hairy in the upper area. Some bracts , which get smaller towards the top, partially surround it. The numerous, fragrant flowers are small, their color is green or reddish brown. The hairless bracts have the same color as the flowers. The ovary is sessile, obliquely spindle-shaped and points diagonally upwards. The sepals are shaped pretty much the same, they are roughly parallel to each other and thus form a tube, only the tips are slightly curved outwards. The dorsal sepal is somewhat concave and fused with the column for a short distance. The lateral sepals have grown together for a short distance at the base and start with a slanted base at the base of the column, where they form a small recess for the nectar. The petals lie against the dorsal sepal and adhere with their inner edges there, their tips are free. The lip is sessile, in some species at the base with two nectar glands pointing backwards. The spread of the lip is runny, the sides are bent upwards and adhere to the column . The column is club-shaped, reaching at the base beyond the point of attachment at the ovary (column foot). The scar is semicircular to bilobed and U-shaped. The stamen is deeply heart-shaped at the base, with a drawn-in tip or rounded at the front. It contains the elongated pollinia that are only loosely stuck together and hang from a shared, centrally located adhesive disc ( Viscidium ). The separating tissue between the stamen and the stigma (rostellum) is just a flat membrane with a small central point. The capsule fruit is inverted ovoid and somewhat asymmetrical.

Occurrence

Mesadenus occurs in two disjoint subregions in tropical America: one in Central America, Mexico, Florida and the Caribbean, and the other in southeastern Brazil. The species grow in relatively dry places in grasslands, savannahs and sparse forests. They occur at altitudes of 2850 meters.

Systematics and botanical history

Mesadenus is classified within the tribe Cranichideae in the subtribe Spiranthinae . The genus was described by Rudolf Schlechter in 1920 . The name is made up of the Greek words μέσος meso , "middle", and ἀδένος adenos , "gland". It refers to the viscidium sitting in the middle of the pollinia. The lectotype is Mesadenus galeottianus , a synonym of Mesadenus polyanthus .

The genus Mesadenus is closely related to some species in the genus Schiedeella . In 1982, Balogh saw Mesadenus only as a section of a broad genus Brachystele .

The genus Mesadenus contains the following species :

  • Mesadenus chiangii (MCJohnst.) Garay : It occurs in the Mexican state of Coahuila .
  • Mesadenus glaziovii (Cogn.) Schltr. : It occurs in the Brazilian state of Rio de Janeiro. It is also called Espinhassoa glaziovii (Cogn.) Salazar & JANBat. placed in the genus Espinhassoa .
  • Mesadenus lucayanus (Britton) Schltr. : It occurs from Mexico to Guatemala and from Florida to the Caribbean.
  • Mesadenus polyanthus (Rchb.f.) Schltr. : It occurs from Mexico to Belize.
  • Mesadenus rhombiglossus (Pabst) Garay : It occurs in the Brazilian state of Minas Gerais. It is also called Espinhassoa rhombiglossa (Pabst) Salazar & JANBat. placed in the genus Espinhassoa .
  • Mesadenus tenuissimus (LOWilliams) Garay : It occurs in the Mexican states of Morelos and Oaxaca.

No longer counted in this genus:

literature

  • James D. Ackerman: Mesadenus . In: Flora of North America Editorial Committee (Ed.): Flora of North America North of Mexico . tape 26 . Oxford University Press, New York and Oxford, S. 525 ( eFloras.org [accessed November 17, 2008] 1993+).
  • Leslie A. Garay: A generic revision of the Spiranthinae . In: Botanical Museum Leaflets of Harvard University . tape 28 , no. 4 , 1982, pp. 335-336 .
  • Alec M. Pridgeon, Phillip Cribb, Mark W. Chase, Finn Rasmussen (Eds.): Genera Orchidacearum. Orchidoideae (Part 2). Vanilloideae . tape 3 . Oxford University Press, New York and Oxford 2003, ISBN 0-19-850711-9 .

Individual evidence

  1. ↑ a b c d e f g h i Rafaël Govaerts (Ed.): Mesadenus. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved March 30, 2020.
  2. ↑ a b Gerardo Salazar: Mesadenus . In: Genera Orchidacearum . Vol. 3, pp. 224-227.

Further information