Flora of the Southeastern United States
2022 Edition

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Key to Trichostema

1 Calyx lobes essentially equal; stamens straight, < 10 mm long; leaves acute to slightly acuminate, the two main lateral veins reconnecting to the midvein near the leaf tip; [section Orthopodium]
1 Calyx strongly bilabiate; stamens strongly arched, 12-20 mm long; leaves obtuse, the two main lateral veins not reconnecting to the midvein; [section Trichostema].
..2 Plants annual; larger leaves 3-7 cm long (including the petiole); plants with long internodes near the base, near-basal branches absent, the best-developed branches from the mid or upper stem; hairs on the upper stem long (0.5-2.0 mm long) or short (0.1-0.4 mm long); [collectively widespread, in a wide variety of habitats, primarily inland, though occasionally occurring as a weed in coastal areas].
....3 Leaves 2.5-4× as long as wide; longer hairs of the upper stem (0.3-) 0.5-2.0 mm long
....3 Leaves 5-15× as long as wide; longer hairs of the upper stem 0.1-0.3 (-0.4) mm long
..2 Plants perennial; larger leaves 1-4 cm long (including the petiole); plants with short internodes near the base, near-basal branches well-developed, these often branching again (except in T. suffrutescens); hairs on the upper stem short (0.1-0.4 mm long); [of the Coastal Plain].
......4 Corolla deep blue (almost black in bud); stems typically virgate, not branched above the base; hairs of the stem not longer at each node; [of peninsular FL, inland as well as on sand ridges near the coasts]
......4 Corolla pastel blue or pink; stems typically rebranching above the base, the plant more-or-less bushy; hairs of the stem longer at the node (in a line between the 2 petioles); [of NC south to s. FL and west to s. MS; restricted to barrier islands, coastal peninsulas, and other maritime situations within 10 km of the ocean]
........5 Anthers lemon yellow; leaves ovate-rhombic, 1-1.5× as long as wide, sessile or subsessile; corolla lavender (definitely with a pinkish tint); bark on older stems dark, tight; plants 1-4 dm tall, forming a tight, compact, hemispheric bush; [of maritime dunes, grasslands, and forest openings from 10 km north of Cape Hatteras (Dare County, NC) south to near Cape Romain (Georgetown County, SC)]
........5 Anthers blue; leaves spatulate, 1.5-3× as long as wide, the petiole relatively well-developed; corolla bluish (lacking a well-developed pinkish tint); bark on older stems yellow to tan, somewhat papery; plants 3-7 dm tall, often gangly and irregularly shaped; [of maritime dunes, grasslands, and coastal scrub from e. GA around the FL peninsula west to s. MS]