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(Last Modified On 3/20/2013)
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(Last Modified On 3/20/2013)
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Genus
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Euphorbia L.
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PlaceOfPublication
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Sp. P1. 450, 1753
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Reference
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Gen. P1. ed 5, 208, 1754.
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Description
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Herbs, shrubs or trees, sometimes succulent, milky latex in all parts; monoecious or rarely dioecious. Leaves opposite, whorled or alternate, often serially on the same plant, simple; sometimes caducous particularly in succulent forms; usually petiolate except in succulents; stipules present or absent, sometimes glandular. Inflorescence a cyathium, the 5 cup-like lobes alternating at their tips with 4-5 glands, these with or without appendages. Staminate flowers in 4-5 cymes, the sub- tending bracteoles partly fused to the involucre or reduced or absent; naked; monandrous; pollen grains subglobose, reticulate to tectate, 3-colporate, sometimes operculate. Pistillate flo'wers terminal, solitary; perianth of 3-6 united sepals or absent; ovary 3-celled each with a single ovule, the styles 3, free or joined basally, usually partly bifid. Fruit. capsular (rarely drupaceous); seed ? ovoid, angled or terete, the surface smooth or variously sculptured, with or without caruncle.
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Habit
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Herbs, shrubs or trees
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Note
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A genus of about 1200 species as used here. The diversity of plant form and detail of the reproductive structures have led a number of workers to suggest that the strong unifying feature of the cyathial inflorescence would better be considered a tribal than a generic character; a number of more "natural" genera would then be formed as segregates of the Linnaean Euphorbia. The most recent discussion of this, a fine account by Webster with a full bibliography (Jour. Arnold Arb. 48: 303-430, 1967), takes the reasonable position that until such segregates can be defined in an unequivocal way they should not be separated as genera even though these would represent evolutionary units. Webster allows that a diagnosis can be made of Chamaesyce and accepts it "diffidently" as a genus, but treats all other segregates which have been proposed as part of Euphorbia L. Much the same disposition is made here. I have less hesitation in accepting Chamaesyce as a distinct genus, and have also accepted Poinsettia at that rank even though in Central America as a whole the boundary between this taxon and Euphorbia subg. Agaloma (Raf.) House is not always distinct. In Panama these two genera are easily distinguishable in the field, and I feel that it is more informative to treat them in this way than to maintain them in Euphorbia L.
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Key
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a. Leaves all whorled; trees or large shrubs; stems articulate .. . 1. E. cotinifolia aa. Leaves alternate, opposite or both, sometimes also with a whorl at one node; herbs, often vining; stems not obviously articulate. b. Capsule glabrous. c. Seed terete, surface smooth; cyathia ca 2 mm diam, the glands 4, dark, the appendages equaling glands, ciliate-pubescent above .................... 2. E. dwyeri cc. Seed strongly angled, surface deeply punctate with pits in regular longi- tudinal rows; cyathia ca 1 mm diam, the glands 4 or 2, green, the appendages obsolete (panamanian specimens) to prominent and white several times size of gland, glabrous ............................................... 3. E. graminea bb. Capsule pubescent, especially when young. d. Leaves ovate to subcordate, rarely larger than 1 X 1 cm; glands usually 4, appendages deeply 3-4 parted; capsule ca 1.5 mm diam; seed ca 1 mm long, surface deeply pitted ......................................... 4. E. ocymoidea dd. Leaves ovate-lanceolate 3.5-6 X 1-2 cm; glands 2, appendages entire or obsolete; capsule ca 3 mm diam; seed ca 2.5 mm long, surface papil- late ......................................... 5. E. oerstediana
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