Euphorbia cornastra

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Euphorbia cornastra
Systematics
Eurosiden I
Order : Malpighiales (Malpighiales)
Family : Spurge Family (Euphorbiaceae)
Genre : Spurge ( Euphorbia )
Subgenus : Chamaesyce
Type : Euphorbia cornastra
Scientific name
Euphorbia cornastra
( Dressler ) Radcl.-Sm.

Euphorbia cornastra is a species of the genus spurge ( Euphorbia ) in the family of Euphorbiaceae (Euphorbiaceae). The species is endemic to Mexico. Hybrids of this type with the closely related poinsettia Euphorbia pulcherrima are offered as ornamental plants in the plant trade. The wild form, however, is very rarely cultivated.

features

Euphorbia cornastra is a woody shrub 1 to 2.5 meters tall, with a short basal trunk that arises from a thickened, bulbous root. The shoot is tomentose when young, balding with age. The branches are hollow. The stalked, dark gray-green leaves sit alternately, sometimes almost opposite or whorled towards the shoots. They are entire or toothed, lanceolate to narrowly ovoid and reach 2 to 6 centimeters in length. Often they are violin-shaped in outline (with two broad triangular lateral lobes, which are separated by a semicircular incision). They are sparsely hairy whitish on the upper side and tomentose on the underside at least on the leaf veins.

The terminal inflorescences are surrounded by a covering of pure white colored bracts , which simulate a flower cover (very similar to that of the closely related poinsettia, which is here red), each of which is up to 13 centimeters in diameter. The bracts are lanceolate, elliptical or narrowly egg-shaped, up to 6 inches long and 0.5 to 2.5 inches wide, with entire margins or toothed. The actual inflorescence is a pleiochasium with three-part axes, the central flower (actually, as typical for milkweed, a reduced inflorescence in the form of a cyathium ) with a 5 to 13 millimeter long stalk, the lateral almost or completely sessile. The marginal cyathia are purely male, the middle bisexual, with a bell-shaped, pentagonal, felt-haired covering. Each cyathium is accompanied by one, occasionally two flattened lip-shaped, yellow-colored nectar glands.

The triangular capsule tears when the fruit ripens and releases the gray-colored seeds, about 10 mm long.

The species is easy to distinguish from Euphorbia pulcherrima , of which there are (rarely) wild forms with a white bract, easy to distinguish in numerous characteristics: among other things, the inflorescence is smaller, the nectar glands differently shaped, the capsule fruit and the seeds are much smaller. In addition, the growth form is different, Euphorbia cornastra remains lower, but is more branched, it forms compact shrubs. All other similar species (of the Poinsettia section ) are herbaceous species.

Unlike the winter-blooming poinsettia, Euphorbia cornastra blooms in midsummer, from mid-July, occasionally until October, in the local rainy season. Seen from a distance, the shrubs resemble the flowering dogwood Cornus florida , which is what the species name refers to.

Distribution and location

Euphorbia cornastra is endemic to the Sierra Madre del Sur , central Guerrero Province , Mexico. There it grows on karst limestone. The species was first found near the small settlement of Cruz de Ocote at almost 2000 meters above sea level in an oak and pine forest.

Systematics

The species was discovered by the American botanist Robert L. Dressler in 1973 and first described in 1975 as Poinsettia cornastra . It was later, like the entire genus, transferred to the genus Euphorbia by the British botanist Alan Radcliffe-Smith . Today, according to morphological and molecular characteristics, it is classified in a section Poinsettia in the (primarily New World) subgenus Chamaesyce of the genus Euphorbia (which is further delimited compared to the traditional genus concept) . According to the genetic data, Euphorbia pulcherrima is closely related and probably the sister species of the poinsettia.

use

The species itself is very rarely cultivated. Crossings with the poinsettia served to change the properties of this long-established ornamental plant. Hybrid breeding lines are characterized by a lighter, mostly salmon-pink colored high-leaf envelope. Since the parents are a summer and a winter flowering species, they bloom intermediately, in autumn. The hybrid Euphorbia pulcherrima x Euphorbia cornastra , known as the cultivar Euphorbia 'Princettia', is therefore marketed in Germany under the name "Herbststern".

swell

  • Robert L. Dressler (1975): Una Poinsettia (Euphorbiaceae) nueva y attractiva de Guerrero (Mexico). Boletín de la Sociedad Botánica de México 35: 17-21. doi: 10.17129 / botsci.1149
  • Alice Le Duc & Mary Lewnes Albrecht (1996): Dogwood Poinsettia (Euphorbia cornastra (Dressler) A. Radcliffe-Smith), a new floral pot crop. HortScience 31 (3): 472.
  • Ya Yang, Ricarda Riina, Jeffery J. Morawetz, Thomas Haevermans, Xavier Aubriot, Paul E. Berry (2012): Molecular phylogenetics and classification of Euphorbia subgenus Chamaesyce (Euphorbiaceae). Taxon 61 (4): 764-789.
  • Laura Trejo, Teresa Patricia Feria Arroyo, Kenneth M. Olsen, Luis E. Eguiarte, Baruch Arroyo, Jennifer A. Gruhn, Mark E. Olson (2012): Poinsettia's wild ancestor in the Mexican dry tropics: Historical, genetic, and environmental evidence . American Journal of Botany 99 (7): 1146-1157. doi: 10.3732 / ajb.1200072 .
  • The wild Poinsettia Page . Instituto de Biología, Universidad Nacional Autónoma de México, 2010.

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