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Key to Euphorbia, Key E: subgenus Esula

Euphorbiaceae

Euphorbia

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1 Principal stem leaves finely serrulate (especially toward the apex); [subgenus Esula, section Helioscopia].
  2 Ovary and capsule smooth
    3 Leaf margins crenulate, the teeth rounded; terminal pleiochasial branches (rays) usually 3 and not or less radiant from above; capsules 1.6-2 mm long; seeds 1.4-1.5 mm long; [endemic to southeastern TX and adjacent LA
    3 Leaf margins serrulate, the teeth pointed; terminal pleiochasial branches (rays) usually 5 and conspicuously radiating from above; capsules 2.5-4 mm long; seeds 1.6-2.2 mm long [uncommon non-native of disturbed areas in e. US]
  2 Ovary and capsule verrucose-roughened.
      4 Plants perennial, with thickened woody taproots; stems villous (often densely so, especially on inflorescence branches); leaves to 25 mm wide; [non-native waif]
      4 Plants annual, rarely biennial, with thin herbaceous to only partially woody taproots; stems glabrous (or occasionally pilose in E. platyphyllos); leaves to 11 mm wide; [natives and waifs].
        5 Leaves sparsely pilose, usually with acute apices; plants usually with 5 terminal pleiochasial branches; [non-native waif, disturbed areas]
        5 Leaves glabrous, usually with obtuse or rounded apices; plants usually with 3 terminal pleiochasial branches; [natives of intact and disturbed areas].
          6 Seeds smooth or very obscurely reticulate, 1.7-2.5 mm long; cyathia with the involucre 1.2-1.5 mm long; involucral bracts typically red; dichasial bracts cordate-clasping
          6 Seeds distinctly alveolate, 1.3-1.8 mm long; cyathia with the involucre 0.6-0.9 mm long; involucral bracts typically yellow; dichasial bracts rounded to subcordate
1 Principal stem leaves entire.
             7 Stem leaves opposite, decussate (each succeeding pair turned by 90 degrees); [subgenus Esula, section Lathyris]
             7 Stem leaves alternate (or mostly so); seeds 1-3 mm long.
               8 Leaves, pleiochasial bracts, and dichasial bracts of similar length throughout the plant; dichasial bracts alternate; pleiochasial branches 3-branched at nodes; cyathia glands lacking divergent, hornlike appendages; [coastal s. FL only]
               8 Leaves and bracts of dissimilar length, not uniform throughout the plant; dichasial bracts opposite; pleiochasial bracts unbranched or 2-branched at nodes; glands of the cyathia with or without hornlike appendages; [widespread, including FL]
                 9 Stem leaves linear to narrowly oblong, averaging ca. 10× as long as wide; [subgenus Esula, section Esula].
                   10 Stem leaves (5-) 10-30 mm long, 0.5-3 mm wide
                   10 Stem leaves 30-80 mm long, 3-8(-12) mm wide
                 9 Stem leaves oblanceolate, oblong, obovate, elliptic, or spatulate, averaging 1-5× as long as wide.
                     11 Seeds smooth, 3-5 mm (E. purpurea) or 1.4-1.6 mm long (E. helleri).
                       12 Primary stem leaves 6-15 mm long; plants taprooted annuals to 30 cm; ovaries glabrous; [LA and TX; section Tithymalus]
                       12 Primary stem leaves (50-) 70-100 cm long; plants robust rhizomatous perennials to 100+ cm tall; ovaries verrucose; [primarily Appalachian; section Helioscopia]
                     11 Seeds pitted or tuberculate, 1.3-2.0 mm long.
                          13 Seeds with one side pitted, the other with longitudinal grooves; [section Tithymalus].
                            14 Stem leaves obovate to suborbiculate, 4-15 mm wide; [widespread, non-native]
                            14 Stem leaves spatulate, 1-4 mm wide; [TX, native]
                          13 Seeds pitted on both faces.
                              15 Ovaries basally pilose; horns (of the glands) either short and blunt OR absent; seeds coarsely pitted with transversely elongate pits in 4 vertical rows; [section Pithyusa]
                              15 Ovaries glabrous; horns (of the glands) slender, elongate, and usually divergent; seeds finely and evenly pitted or tuberculate; [section Tithymalus].
                                16 Seeds tuberculate
                                16 Seeds finely pitted with numerous, evenly distributed, isodiametric pits.
                                  17 Dichasial bracts connate 1/4-1/2 of their length (often only on one side).
                                    18 Petioles 0-3 mm long; capsules ovoid-globose, 2.6-2.7 mm long; seeds with deep, rounded pits in 3-4 regular, vertical rows; [Interior Highlands of AR, e. OK, and s. MO; disjunct in c. TN]
                                    18 Petioles 2-5 mm long; capsules subglobose, 2-2.5 mm long; seeds with scattered, deep and broad pits; [TX]
                                  17 Dichasial bracts usually distinct, occasionally subconnate basally.
                                       19 Dichasial bracts strongly imbricate; seeds gray to purple-gray or sometimes nearly black
                                       19 Dichasial bracts not imbricate; seeds white to gray or red-brown to brown.
                                         20 Biennial or occasionally annual herbs; petioles of lower stem leaves 5-10 mm long; leaf blades usually oblanceolate to obovate, rarely ovate, 3-10 mm wide (at least some blades more than 5 mm wide); capsules 2.5-3.2 mm long.
                                         20 Annual herbs; petioles of lower stem leaves 0-2 mm long; leaf blades linear to oblanceolate, spatulate-cuneate, or slightly lanceolate, 0.5-5 mm wide; capsules 1.8-2.4 mm long.
                                           21 Seeds reddish brown to brown, 1.3-1.4 × 0.8-0.9 mm, with 4-6 shallow pits or irregular oblong grooves on adaxial faces, small-pitted or nearly smooth on abaxial faces.
                                           21 Seeds white to gray, 1.4-1.7 × 1-1.6 mm, with pits scattered over entire surface.
                                             22 Leaf blades oblanceolate, 3-5 mm wide; seeds ovoid, 1.6-1.7 × 1.4-1.6 mm; [granitic outcrops, GA].
                                             22 Leaf blades linear to slightly lanceolate or linear-oblanceolate, 0.5-2.5 mm wide; seeds ellipsoid, 1.4-1.7 × 1.0-1.3 mm; [sandy soils, TX Coastal Plain].
                                               23 Stems 10-22 cm tall; leaf blades linear-oblanceolate, apices rounded; dichasial bracts reniform-ovate to subdeltate-ovate, bases truncate; seeds 1.6-1.7 × 1.1-1.3 mm, the surfaces with regular concave depressions; [Atascosa, Bexar, Wilson counties, TX].
                                               23 Stems 6-13 cm tall; leaf blades linear to slightly lanceolate, apices acute; dichasial bracts broadly ovate-lanceolate, bases rounded; seeds 1.4-1.5 × 1-1.1 mm, the surfaces with irregular, not obviously concave depressions; [Jim Hogg, Kenedy counties, TX]