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3. Amsonia Walter, Fl. Carol. 11, 98. 1788.
Blue-star [Probably for Dr. John Amson, eighteenth-century physician in Williamsburg, Virginia, serving as its mayor 1750 and 1751]
Linh Tõ Ngô
Wendy L. Applequist
Herbs, perennial; latex milky. Stems usually erect and clumping, unarmed, glabrous or pubescent with eglandular hairs. Leaves deciduous, alternate or subverticillate, petiolate or sessile, reduced in size toward stem base, usually at least slightly heteromorphic with branch leaves proportionately narrower than main stem leaves; stipular colleters absent; laminar colleters absent. Inflorescences terminal, thyrsoid or corymbose cymes, distal branches occasionally terminated by small inflorescences that almost never set fruit, pedunculate. Flowers: calycine colleters absent; corolla blue to purplish, white, or lavender (pink), salverform, aestivation sinistrorse; corolline corona absent; androecium and gynoecium not united into a gynostegium; stamens inserted near top of corolla tube; anthers not connivent, not adherent to stigma, connectives not appendiculate, locules 4; pollen free, not massed into pollinia, translators absent; nectary absent or annular. Fruits follicles, paired, brown, slender, terete or moniliform, smooth, glabrous or rarely with patchy indument. Seeds cylindric, fusiform, or ± terete, not winged, not beaked, not comose, not arillate. x = 11.
Species 17 (15 in the flora): United States, n Mexico, Europe (Greece, Turkey), e Asia.
Amsonia is taxonomically problematic. Species of the southeastern and south-central United States are highly variable with, in some cases, no definitive species or varietal boundaries and persistent nomenclatural issues. Southwestern species are often variable and sometimes very similar to other species. This treatment conservatively maintains the species circumscriptions that were favored by S. P. McLaughlin (1982), except as noted. Three subgenera are recognized in this treatment, reduced from four in some recent literature. The southwestern subg. Articularia and Sphinctosiphon are most distinguishable in fruit, at which time some species of subg. Sphinctosiphon are hard to distinguish from one another.
SELECTED REFERENCE McLaughlin, S. P. 1982. A revision of the southwestern species of Amsonia (Apocynaceae). Ann. Missouri Bot. Gard. 69: 336–350.
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Corolla tubes broadest at apex, not constricted; stigmas depressed-capitate to truncate; bracts on distal portions of inflorescences usually inconspicuous, to 2.5 mm, narrowly deltate to deltate or ovate; sc, se United States, Kansas to Virginia, s to e Texas to Florida |
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3a Amsonia subg. Amsonia, p. 113 |
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Corolla tubes slightly narrowing to conspicuously constricted at apex; stigmas apiculate with 2 small lobes; bracts on distal portions of inflorescences usually conspicuous, mostly 2–6 mm, linear to narrowly deltate (in A. jonesii usually short, those subtending individual flowers often less than 1 mm or absent); sw United States to c Texas. |
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(2) |
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| 2 (1) |
Stems usually branched for most of length (sometimes only distally); corolla tubes (7–)8–12(–13) mm, moderately to strongly constricted in narrow band just below apex (most visible just before anthesis); mature follicles moniliform, strongly constricted between seeds; seeds fusiform with acute to rounded-acute or flat-truncate (rarely diagonally truncate) ends, with mostly smooth surface |
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3b Amsonia subg. Articularia, p. 118 |
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Stems usually branched only on distal portion (sometimes to near base, rarely unbranched); corolla tubes (6–)7.5–41(–45) mm, broadest below apex, slightly narrowing to moderately constricted at apex; mature follicles terete, at most slightly narrowed between seeds; seeds cylindric with diagonally truncate to flat-truncate ends, with mostly convoluted surface |
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3c Amsonia subg. Sphinctosiphon, p. 120 |
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List of lower taxa
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