Stegolepis

from Wikipedia, the free encyclopedia
Stegolepis
Stegolepis guianensis at the foot of the Roraima-Tepui in Venezuela

Stegolepis guianensis at the foot of the Roraima-Tepui in Venezuela

Systematics
Monocots
Commelinids
Order : Sweet grass (Poales)
Family : Rapateaceae
Subfamily : Saxofridericioideae
Genre : Stegolepis
Scientific name
Stegolepis
Klotzsch ex grain.

Stegolepis is a genus inthe Rapateaceae family . It is native to northern South America, especially Venezuela and the Guyana highlands. There it is mainly found on sandstone tepuis .

description

Species of the genus Stegolepis are perennial , herbaceous plants . Some species are epiphytes , most of them live terrestrially . The largest species, Stegolepis grandis , can reach heights of growth of up to three meters. The shoot axes are thickened (caudiciform) and little or no branching. They are short, often heavily thickened on one side and flattened on the other. Usually they are covered by dead old leaves. Massive rhizomes are formed underground .

The leaves are narrow-lanceolate and sword-shaped or grass-like. Leaf auricles are absent or developed.

During the flowering period, several axillary long shoots are formed, up to three meters long in Stegolepis grandis , on which a large number of spatulate bracts are formed, which tightly envelop the inflorescences . Except for the species of the Gleasoninana subsection, the bracts are stunted to a narrow, thin, dry membrane. Pre-leaves are present and, except for the species of the Gleasoninana subsection, overlap in a graded manner .

The sepals are fused to form a short tube (tube), but the tips protrude, in the pauciflora section they are bent back. The petals are differentiated into a flag and a nail. The nails form a tightly woven tube, the shape of the flag is variable.

The flowers have six stamens . The stamens are free, or more often fused at the base. If it has grown together to form a tube, it is free or has grown together with the nail of the crown. More rarely, it has grown together with the sepal or flag opposite to form a simple tube.

The anthers are four-ocular. The elongated base is thickened. They open at the end with one or two pores. After opening, the counters form a hood-like extension. The pollen grains are elongated and monosulcat, that is, they have only one furrow. This extends over 4/5 of the pollen axis, which is 29 to 43 micrometers long. The exine is fine-grained, reticulated.

Three fused carpels form an upper ovary with fused central placentation . There are fruit capsules formed. The seeds are prismatic or pyramidal. The seed coat is often deepened or fluted like a trough, and is usually light in color.

ecology

The flowers do not produce nectar and are pollinated by bees ( melittophilia ) in the form of vibration pollination . Beetles from the superfamily Curculionoidea are often found in the flowers of Stegolepis parvipetala . In Stegolepis angustata it has been observed that the empty anthers are chewed up by bees of the Halictidae family .

Most Stegolepis species are able to survive at least light fires. The burnt leaves are then replaced by new ones growing out of the caudiciform trunk. If the stem is no longer there, the plant often survives in the rhizomes.

Distribution and locations

The distribution area of ​​the genus is in northern South America and Panama.

The Stegolepis species grow in open, moist and swampy locations, often on rocky ground. They are seldom found in open forests. Locations are found mainly at medium altitudes and in mountains in the highlands of Guiana , especially on sandstone tepuis . Most of the endemic species are found on only one or a few tepuis, on which more than one species is rarely found.

Systematics and evolution

It is likely that the genus Stegolepis originated 12 million years ago and the individual species separated 6 million years ago. Today 31 species belong to the genus Stegolepis , in three sections . However, molecular biological studies have shown that the genus is likely to be paraphyletic . In particular, some species from the Pauciflorae and Guianenses sections seem to be more closely related to species of the genera Amphiphyllum and Marahuacaea than to Stegolepis species from the Pungentes section . These in turn form a polytome group with epidryos . In order to achieve monophyly, the genus would have to be separated into three new genera. The following cladogram shows the intertwined relationships :






Stegolepis sect. Pauciflorae


   

Stegolepis sparkling wine. Guianenses



   

Amphiphyllum



   

Marahuacaea



   

Epidryos


   

Stegolepis sparkling wine. Pungentes


Template: Klade / Maintenance / 3

The system of the genus follows the flora of Venezuela :

Species described since 1982 that are not assigned to any section are:

literature

  • Bassett Maguire: Rapateaceae . In: Flora of Venezuela . tape 11.2 . Inst. Botanico, Caracas 1982, p. 115-116 .
  • TJ Givnish, M. Evans, ML Zjhra, TB Patterson, PE Berry, KJ Sytsma: Molecular Evolution, Adaptive Radiation, and Geographic Diversification in the Amphiatlantic Family Rapateaceae: Ecidence from ndhF Sequences and Morphology . In: evolution . tape 54 , no. 6 , 2000, pp. 1915-1937 ( pdf ).

Individual evidence

  1. after Givnish et al., 2000.
  2. a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Rafaël Govaerts (Ed.): Stegolepis. In: World Checklist of Selected Plant Families (WCSP) - The Board of Trustees of the Royal Botanic Gardens, Kew . Retrieved August 16, 2018.