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Trichostema
See list of 3 species in this genusTrichostema is often defined as excluding Isanthus based on floral differences. However, phylogenetic research showed that Isanthus is properly part of the genus Trichostema (Huang 2002).
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1a. Calyx ± actinomorphic; stamens nearly straight or weakly arched, shorter than 10 mm; 2 principal lateral veins of leaf blade reconnecting to midvein
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1b. Calyx zygomorphic; stamens conspicuously arched [Fig. 707], 12–20 mm long; 2 principal veins of leaf blade not reconnecting to midvein or the lateral veins absent altogether
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2a. Leaf blades oblong or elliptic to ovate, 5–25 mm wide, 2.5–4 times as long as wide; longer hairs of upper stem (0.3–) 0.5–2 mm long; mericarps 1.9–2.3 mm long
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2b. Leaf blades linear, 1–5 mm wide, 5–15 times as long as wide; longer hairs of upper stem 0.1–0.3 (–0.4) mm long; mericarps 1.6–1.8 mm long
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Each photo represents one species in this genus.