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FNA | Family List | FNA Vol. 14 | Apocynaceae

33c. Amsonia Walter Sphinctosiphon (K. Schumann) Woodson, Ann. Missouri Bot. Gard. 15: 411. 1928.

Amsonia sect. Sphinctosiphon K. Schumann in H. G. A. Engler and K. Prantl, Nat. Pflanzenfam. 120–122[IV,2]: 143. 1895

Stems branched usually only on distal portion, less often to near base (rarely unbranched). Bracts on distal portions of inflorescences linear to narrowly deltate, mostly 2–6 mm (occasionally shorter; in A. jonesii often less than 1 mm, those below individual flowers deltate or absent). Flowers: corolla tube (6–)7.5–41(–45) mm, slightly narrowing to moderately constricted at apex; stigma apiculate with 2 small lobes. Follicles terete, not strongly constricted between seeds. Seeds brown, cylindric and diagonally truncate to flat-truncate, with mostly convoluted surface.

Species 8 (8 in the flora): sw, sc United States, n Mexico.

The circumscription of subg. Sphinctosiphon in this treatment includes three long-flowered species that in previous treatments were segregated within subg. Sphinctosiphon as sect. Longiflora Woodson or removed into “subg. Longiflora” (not validly published) by S. P. McLaughlin (1982). These species are not otherwise distinguishable as a group from the usually shorter-flowered species of subg. Sphinctosiphon, so they are most conservatively treated as simply the largest-flowered species of that subgenus. The key emphasizes vegetative features where possible; fruit morphology does not distinguish most species, and fruiting specimens may be difficult to identify.

1 Stems glabrous.   (2)
+ Stems sparsely to moderately pubescent (glabrate, densely pubescent).   (7)
       
2 (1) Stem leaf blades ovate to lanceolate, elliptic, or narrowly oblong, (6–)9–25(–32) mm wide.   (3)
+ Stem leaf blades linear to ligulate (to somewhat narrowly elliptic or lanceolate), (0.7–)1–7(–9) mm wide.   (4)
       
3 (2) Stem leaf blades ovate to lanceolate or somewhat elliptic; branch leaf blades lanceolate (narrowly elliptic), 2.2–3.9 cm; sepals (0.3–)1–2.5(–4) mm; corolla tube (6–)7.5–8.5(–10) mm, lobes blue, (4–)5–7(–8.5) mm   10 Amsonia jonesii (in part)
+ Stem leaf blades narrowly oblong to lanceolate; branch leaf blades very narrowly lanceolate or elliptic to linear, 3.5–6(–6.8) cm; sepals (2–)3–5(–7) mm; corolla tube 7.5–12(–17) mm, lobes blue or white, (2.5–)3–5(–7) mm   13 Amsonia palmeri (in part)
       
4 (2) Stem leaf blades (2.3–)3–6.5(–9) cm × (0.7–)1–2.8(–5) mm; corolla tubes (20–)28–41(–45) mm   12 Amsonia longiflora (in part)
+ Stem leaf blades 3.2–12(–14) cm, usually 3+ mm (in A. palmeri as little as 2 mm) wide; corolla tubes 7.5–21.5 mm.   (5)
       
5 (4) Corolla tubes 7.5–12(–17) mm, lobes (2.5–)3–5(–7) mm; Arizona, New Mexico, Texas   13 Amsonia palmeri (in part)
+ Corolla tubes (13–)14–21.5 mm, lobes (5–)7–14(–16) mm; Arizona.   (6)
       
6 (5) Stem leaf blades (5.5–)7–12(–14) cm; corolla tubes 16–21.5 mm, lobes white to bluish, turning blue with age, 9.5–14(–16) mm; fruits 4–12(–15) cm; s Arizona   9 Amsonia grandiflora
+ Stem leaf blades 3.2–7.3(–9.3) cm; corolla tubes (13–)14–17(–19) mm, lobes white, (5–)7–9(–10) mm; fruits (2–)3–7(–10) cm; n Arizona   14 Amsonia peeblesii
       
7 (1) Stem leaf blades linear to ligulate (very narrowly elliptic or lanceolate), (0.7–)1–2.8(–5) mm wide; corolla tubes (20–)28–41(–45) mm   12 Amsonia longiflora (in part)
+ Stem leaf blades narrowly oblong-elliptic, narrowly elliptic, narrowly lanceolate, lanceolate, ligulate, linear, or ovate, 2–25(–32) mm wide; corolla tubes (6–)7.5–23 mm.   (8)
       
8 (7) Branches few or absent, if present usually remaining shorter than infructescences; stem leaf blades ovate to lanceolate (elliptic, narrowly elliptic), (2–)3.3–5.5(–6.1) cm × (6–)9–25(–32) mm, surfaces glabrous; branch leaf blades lanceolate (narrowly elliptic), 3–9(–10) mm wide; sepals narrowly deltate to deltate (subulate, broadly deltate), (0.3–)1–2.5(–4) mm; corolla tubes (6–)7.5–8.5(–10) mm, lobes blue; Arizona, Colorado, New Mexico, Utah   10 Amsonia jonesii (in part)
+ Branches present, usually elongating to slightly exceed or at least equal infructescences; stem leaf blades variable in shape and size, sometimes lanceolate but not ovate, to 18 mm wide, surfaces usually at least sparsely pubescent on midrib; branch leaf blades variable, in some linear to ligulate; sepals subulate to narrowly deltate, (2–)3–6(–7) mm; corolla tubes 7.5–23 mm, lobes white to greenish or yellowish white, cream, or blue; Arizona, New Mexico, Texas.   (9)
       
9 (8) Branch leaf blades narrowly lanceolate, (3–)6–9 mm wide; corolla tubes 12–14(–15) mm, lobes (2–)3–4 mm; seeds 3–4(–4.8) mm diam.; Baboquivari Mountains, Pima County, Arizona   11 Amsonia kearneyana
+ Branch leaf blades linear to ligulate or very narrowly lanceolate, oblong, or elliptic, 1–5(–7) mm wide; corolla tubes 7.5–23 mm, lobes (2.5–)3–11(–13) mm; seeds (1–)2–3 mm diam.; Arizona, New Mexico, Texas.   (10)
       
10 (9) Corolla tubes (16–)18–23 mm, lobes (6.5–)8–11(–13) mm; Socorro County, New Mexico   8 Amsonia fugatei
+ Corolla tubes 7.5–17 mm, lobes (2.5–)3–9(–12) mm; Arizona, New Mexico, Texas.   (11)
       
11 (10) Stems 23–62(–80) cm, erect; corolla tubes 7.5–12(–17) mm; corolla lobes (2.5–)3–5(–7) mm, adaxial surface glabrous   13 Amsonia palmeri (in part)
+ Stems 10–20(–50) cm, usually erect, with long stems always ascending; corolla tubes (11–)12–17 mm; corolla lobes (5–)6–9(–12) mm, fre­quently pubescent at base of adaxial surface   15 Amsonia tharpii


 

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