Oxygonum pterocarpum Osborne & Vollesen

This species is accepted, and its native range is Tanzania.


Harley, R.M. 2015. “Oocephalus lythroides” (Lamiaceae: Ocimeae: Hyptidinae) from the Distrito Federal of Brazil is a new species: Oocephalus grazielae. Kew Bulletin 70: 18. DOI https://doi.org/10.1007/s12225-015-9568-7

Oxygonumpterocarpum is known only from the two collections cited, occurring within a very restricted area delimited by the coordinates given above. In the first locality only 5 – 10 individual plants were observed but in the second (the type locality) well over 100 individuals were seen. The area where it occurs has no human settlements as it forms part of the corridors between the Ruaha National Park/Rungwa Game Reserve to the east and Ugalla Game Reserve/Katavi National Park to the west. At present these corridors are deliberately kept empty of human habitation and there are still large numbers of elephants, lions and other game in this area. The Brachystegia-Julbernardia woodlands are harvested for timber but the grasslands are only used for occasional grazing. At the moment there seem to be no serious threats to the status of these corridors but with the ever increasing human population in Tanzania, which currently has an annual population growth rate of 3.1 % (UNdata2014), there is always the possibility that pressure might increase to the point where human settlement starts. The two localities are relatively close to Rungwa Game Reserve to the east and Katavi National Park/Ugalla Game Reserve to the west. Both these reserves contain numerous areas with similar habitats which have not been at all well botanised. Were the species to be recorded in either of these its future could be considered to be reasonably safe. However, in view of the very limited information on this species at present it is difficult to give a reasonable conservation assessment and we classify it as Data Deficient (DD) according to the categories and criteria of IUCN (2001).
Known only from the two collections cited below. Both are from a restricted area in Sikonge Distr. in the southern part of Tabora Region in W Tanzania occurring within the Zambesian Regional Centre of Endemism as defined by White (1983).
Large, seasonally wet, open areas (dambos) in tall, mature woodland. These areas are covered with open Combretum adenogonium-Diospyros kirkii-Acacia seyal wooded grassland and have a fairly short, open grass cover. They stand on dark grey, shallow, sandy-peaty soils overlying ironstone pans and are regularly inundated in the rainy season. The surrounding Brachystegia woodland, usually only reaching 1 – 2 m above the grass sward, stands on deep, greyish-brown sandy soils and is never inundated.
Morphology General Habit
Erect, glabrous, perennial herb to 65 cm tall with thick, woody rootstock; stems 1 – several from the base, striate, few-branched, usually with 1 – 2 leafy nodes; internodes 6 – 15 cm long
Morphology Leaves
Leaves fleshy, basal and cauline (mostly in a basal cluster); basal leaves erect, linear-lanceolate, often with the widest part of the lamina located at the distal half, 10 – 25 × 0.3 – 1.2 cm, decurrent at the base, without distinct petiole, apex acute, margin entire; cauline leaves in clusters of 2 – 6 at nodes, similar to basal leaves but smaller, 6 – 14 × 3 – 6 cm
Morphology Reproductive morphology Flowers
Flowers hermaphrodite, heterostylous; perianth white, 8 mm long with tube 3 mm long and five obovate lobes 5 × 2 mm, obtuse at apex; stamens and pistil included
Morphology Reproductive morphology Flowers Androecium Stamens
Stamens 8, in two whorls, the 5 outer stamens alternating with perianth lobes, inserted at apex of perianth tube and glabrous at base; the 3 inner stamens inserted in perianth tube and densely villous at base; filaments in brevistylous flowers 4 – 5 mm long, in longistylous flowers 1.5 – 2 mm long; anthers 0.3 – 0.45 × 0.25 – 0.35 mm
Morphology Reproductive morphology Flowers Gynoecium Ovary
Ovary 0.3 – 0.35 mm long; styles 3, connate at base, in brevistylous flowers styles 2.5 mm long, connate for 1 mm, in longistylous flowers styles 5 mm long, connate for 2 mm; stigmas capitate
Morphology Reproductive morphology Fruits
Fruit pale yellowish-green, 8 – 10 × 5 – 6 mm, with marcescent corolla at apex, fusiform, trigonous, obovate in outline, with 3 wings on the angles 2 mm wide and with a transverse ridge running around the fruit just over half way from the base, sometimes forming a minute tooth at the margin of each wing and several minute teeth between the wings
Morphology Reproductive morphology Inflorescences
Inflorescence 25 – 32 cm long, consisting of 1 – 3 slender, erect, terminal thyrses; axis narrowly winged towards the apex; bracts 5 – 10 mm long, tubular to obconical with a narrowly acuminate, setose apex and several shorter lateral setae, chartaceous at apex between the setae; flowers 4 – 5 per bract with 1 flower per bract open at a time; pedicels erect, 5 – 7 mm long, becoming thicker and up to 8 mm long in fruit
Morphology Stem
Ocreae 7 – 20 mm long, chartaceous and reddish-brown on dried specimens, apex truncate, with a fringe of fine setae 3 – 10 mm long
Oxygonumpterocarpum can be distinguished from all other species of Oxygonum by the combination of its long, erect, entire and linear-lanceolate basal cluster of leaves and distinctive, pale yellowish-green, 3-winged fruits (Fig. 1). The winged fruits of O. pterocarpum most closely resemble those of the annual O. alatum Burch., from which it clearly differs by its perennial habit and its basal cluster of erect, entire leaves (the leaves of O. alatum being cauline and often lobed). The specific epithet refers to the winged fruit (from the Greek pterón — wing and karpos — fruit). There is no current infrageneric classification in Oxygonum within which to place the new species and additionally, it does not appear to be closely related to any other Oxygonum species. The unusual, erect, linear-lanceolate, long basal foliage of O. pterocarpum is particularly striking in comparison with all other Oxygonum species. Foliage in Oxygonum tends to be cauline and although variable in shape, is usually much shorter than that of O. pterocarpum. The winged fruits of O. pterocarpum are also distinctive. They appear closest to those of O. alatum (see Recognition above) but differ in shape, as the fruits of O. alatum are ovate in outline while those of O. pterocarpum are obovate. A carefully sampled molecular phylogeny is needed to understand the relationships within Oxygonum.
Type: Tanzania, Sikonge Distr., 56 km on Ipole-Rungwa road, 10 Feb. 2009, Bidgood, Leliyo & Vollesen 7737 (holotype NHT!; isotypes BR!, EA!, K!, MO!, P!).

Native to:


Oxygonum pterocarpum Osborne & Vollesen appears in other Kew resources:

Date Reference Identified As Barcode Type Status Has image?
Bidgood, S. [7737], Tanzania K001089679 isotype Yes
Bidgood, S. [7737], Tanzania K001089680 isotype Yes

First published in Kew Bull. 70(2)-21: 2 (2015)

Accepted by

  • Govaerts, R., Nic Lughadha, E., Black, N., Turner, R. & Paton, A. (2021). The World Checklist of Vascular Plants, a continuously updated resource for exploring global plant diversity. https://doi.org/10.1038/s41597-021-00997-6. Scientific Data 8: 215.


Kew Bulletin

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  • Herbarium Catalogue Specimens

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    The International Plant Names Index and World Checklist of Selected Plant Families 2022. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

  • Kew Bulletin

    Kew Bulletin

  • Kew Names and Taxonomic Backbone

    The International Plant Names Index and World Checklist of Selected Plant Families 2022. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
    © Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0