Xenostegia

Accepted name/Authority/Place of publication: 

XENOSTEGIA D. F. Austin & Staples, Brittonia 32: 533. 1980

Tribe: 
Merremieae
Synonyms: 

Merremia sect. Halliera O'Donell, Lilloa 6: 472. 1941.

Type Species: 

Xenostegia tridentata (L.) D.F. Austin & Staples.

Habit: 
Perennial herbs; stems prostrate, tips twining.
Leaves: 
Leaves petiolate, linear, oblong-linear, lanceolate-elliptic, or oblanceolate to spathulate, base hastate; basal lobes clasping stem, dentate or entire, apex acute to emarginate, mucronate, or tridentate.
Inflorescences: 
Inflorescences axillary, cymose, 1- or 2-(or 3)-flowered.
Flowers: 
Flower sepals oblong or oblong-ovate, subequal to unequal, acute or obtuse; inner 3 sepals narrower, apically tapering into slender points, all enlarged in fruit; corolla pale yellowish or whitish, often with a purplish centre, broadly funnelform or campanulate; stamens included, anthers not twisted at dehiscence; pollen globose, pantoporate, not spiny; pistil included, ovary 2-celled, 4-ovuled, style 1, filiform, stigmas 2-globular.
Pollen: 
Pollen globose, pantoporate, not spiny.
Fruits: 
Capsule 4-valved, glabrous or pubescent apically.
Seeds: 
Seeds 1–4, ovoid-trigonous, brownish to black.
Distribution: 

Tropical regions of Asia, Africa, Australia and the Pacific; introduced and naturalized on Puerto Rico in the Caribbean. map

Phylogeny: 

Xenostegia tridentata is extraordinarily variable, which has led to naming of many taxa based on seemingly distinctive morphotypes. In Africa 3 infraspecific taxa are recognized; in Asia all the variation is accommodated in a single polymorphic species. In contrast, X. medium is rather constant in its morphology and is easily distinguished from its congener by the enlarged outer sepals.

Number of Species: 
2
Commentary: 

Long included in the polyphyletic genus Merremia, these 2 species are distinctive in terms of pollen apertures, seed germination, cotyledon shape, stigma micromorphology, and seed characters; in 1981 they were segregated as genus Xenostegia.

References: 

Austin & Staples, Brittonia 32: 533-536. 1980.

R.C. Fang & Staples in C.Y. Wu & P.H. Raven (eds.), Fl. China 16: 300. 1995.

Lejoly & Lisowski, Fragm. Flor. Geobot. 38: 379. 1993.

Author/Editor

Author: 
G.W. Staples
Editor: 
G. Staples & Esmond Er
Publication: 

Flora of Thailand 10(3): 464-467. 2010.

Contributors: 
Classification: 
Xenostegia
Mon, 2011-07-18 02:25 -- Esmond
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