Euphorbia williamsonii L.C. Leach

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Soil pockets on rocky outcrops
Ntumbachusi Falls
Mar 2019
Photo: Nick Wightman

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Synonyms:
Common names:
Frequency:	Locally common
Status:	Native
Description:	Succulent shrub up to 1 m high branching from a partially exposed tuberous root; branched erect and rarely rebranching, acutely 3-angled, slightly constricted into variable shaped segments 2.5-5 x 2.5-5.25 cm, ±obovate to subcircular; angles crenulated with tubercles to 18 mm apart along the margins, or further apart just above the constriction; spine shields ±obovate, forming a ± continuous horny margin along the angles, 1-2.5 mm wide; spines to 1 cm long, diverging; prickles rudimentary; secondary rudimentary spines often flanking the flowering eye; leaves c. 2 x 1.5 mm, ovate, caduceus; cymes solitary, simple or reduced to single cyathia; peduncle 1.5-5.5 x 5.75 mm; bracts c. 2.5 x 5.5 mm, semicircular, blackish-red; cyathia to 3 x 5-7 mm with funnel-shaped involucres, bright red; glands 5(6), 1.5 x 2.5-4 mm, transversely elliptic, yellowish with reddish margin; lobes 1.5 x 2-2.5 mm, transversely oblong, finbriate, dark red; male flowers: c. 60: bracteoles numerous, fimbriate stamens c. 5.5 mm long; female flowers: styles stout, 2.5-3 mm long, spreading recurved, united at base, stigmas capitate; capsule to 5.5 x 9.5 mm, obtusely lobed, subsessile, shiny bright red; seeds c. 3.5 x 3 mm, subglobose, smooth, brown.
Type location:	Zambia, Kawambwa
Notes:
Derivation of specific name:	williamsonii: named after Graham Williamson, who collected across Zambia and collected the type specimen together with Brain Simon.
Habitat:	In fibrous mats on rocky quartzite outcrops.
Altitude range:	1150 m (approx)
Flowering time:	Nov - Mar
Worldwide distribution:	Only known from type locality at Ntumbachusi Falls in northern Zambia.
Zambian distribution (Flora Zambesiaca):	N
Zambian distribution (Provinces):	Lp
Growth form(s):
Endemic status:	Endemic
Red data list status:	Data deficient
Insects associated with this species:
Spot characters:	Display spot characters for this species
Content last updated:	Wednesday 10 April 2019
Literature:	Carter, S. & Leach, L.C. (2001). Euphorbiaceae: subfamily Euphorbioideae: tribe Euphorbieae Flora Zambesiaca 9(5) Pages 404 - 405.

Other sources of information about Euphorbia williamsonii:

External websites:

African Plants: A Photo Guide (Senckenberg): Euphorbia williamsonii
BHL (Biodiversity Heritage Library): Euphorbia williamsonii
EOL (Encyclopedia of Life): Euphorbia williamsonii
GBIF (Global Biodiversity Information Facility): Euphorbia williamsonii
Google: Web - Images - Scholar
iNaturalist: Euphorbia williamsonii
IPNI (International Plant Names Index): Euphorbia williamsonii
JSTOR Plant Science: Euphorbia williamsonii
Mansfeld World Database of Agricultural and Horticultural Crops: Euphorbia williamsonii
Plants of the World Online: Euphorbia williamsonii
Tropicos: Euphorbia williamsonii
Wikipedia: Euphorbia williamsonii