Hymenoxys odorata
Hymenoxys texana
bitter hymenoxys, bitter rubberweed, fragrant bitter weed, poison rubberweed, western bitterweed
prairiedawn
1–25, usually purple-red-tinted proximally, sometimes throughout, often branched throughout, ± hairy.
1–7, purple-red-tinted proximally or throughout, unbranched or branched distally, glabrous or sparsely hairy.
blades simple or lobed (lobes 3–19+), ± hairy, gland-dotted;
mid leaves lobed (lobes 5–11+, terminal lobes 0.3–1 mm wide).
blades simple or lobed (lobes 3–5, ultimate margins entire or pinnately toothed), glabrous or sparsely hairy, weakly to moderately gland-dotted;
mid leaves sometimes lobed (terminal lobes 1–2.5 mm wide).
2–12 cm, sparsely hairy.
0.5–1.5 cm, glabrous or sparsely hairy.
subhemispheric to campanulate to ± urceolate, 6–10 × 7–12.5 mm.
campanulate to ± urceolate, 5–7 × 6–8 mm.
8–13;
corollas yellow, 8.5–11 × 3–5.5 mm.
6–8;
corollas yellow, 2–3 × 0.7–1 mm (not surpassing phyllaries).
50–150+;
corollas 2.6–4.1 mm.
40–75+;
corollas 1.5–2.1 mm.
in 2 series, unequal;
outer 8–13, basally connate 1/4–1/3 their lengths, obovate to oblanceolate, 3.5–5.2 mm, apices acuminate;
inner 8–13, obovate, 3.8–5.9 mm, apices acuminate to acute.
in 2 series, unequal;
outer 6–8, distinct or weakly basally connate, obovate or oblanceolate to lanceolate, 4–4.7, apices obtuse to acute;
inner 6–8, obovate to ovate, 4–4.5 mm, apices usually acute.
15–350+ per plant in paniculiform arrays.
1–30 per plant, borne singly or in paniculiform arrays.
narrowly obpyramidal, 1.7–2.5 mm;
pappi of 5–6 obovate, aristate scales 1.6–2.3 mm.
obpyramidal to narrowly obpyramidal, 1.5–1.8 mm;
pappi of ca. 5 obovate, aristate scales 1.4–1.8 mm.
= 22, 24, 28, 30.
= 6, 16.
Hymenoxys odorata
Hymenoxys texana
Of conservation concern.
Hymenoxys texana is known only from open grassy areas at relatively few localities within 150 km or so of Houston.
Morphology and DNA restriction site data clearly associate this species with Hymenoxys; its relationships to other taxa in the genus are unclear (M. W. Bierner and R. K. Jansen 1998). Furthermore, unlike Hymenoxys and like Tetraneuris, H. texana possesses monoterpene glycosides and lacks seco-pseudoguaianolides (O. Spring et al. 1994). Also, its very unusual chromosome numbers of 2n = 6 and 16 (J. L. Strother and L. E. Brown 1988) are unlike any reported from other taxa in either Hymenoxys or Tetraneuris (mainly 2n = 30 with some dysploidy and polyploidy; Bierner 1994). Despite the conflicting data, Bierner and Jansen, and Bierner (2001) maintained it in Hymenoxys, but separated it from the other members of the genus in its own subgenus.
Hymenoxys texana is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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