Gayophytum heterozygum
Onagraceae tribe Onagreae
zig zag gayophytum, zigzag groundsmoke
erect, usually unbranched near base, branched at each of several nodes proximal to first flower, less branched distally, branching dichotomous, 15–80 cm.
much reduced distally, 15–60 × 1–5 mm;
petiole 0–10 mm;
blade narrowly lanceolate to sublinear.
alternate or basal;
stipules absent.
with flowers arising usually as proximally as first 10–20 nodes from base.
sepals 1–1.8 mm, reflexed singly or in pairs;
petals 2–3(–4) mm;
pollen ca. 50% fertile;
stigma hemispheric to subglobose, surrounded by anthers at anthesis.
usually actinomorphic, rarely slightly zygomorphic (in Oenothera), (3 or)4-merous;
stamens 2 times as many, or rarely as many, as sepals;
pollen usually shed in monads, rarely tetrads (Chylismia sect. Lignothera).
a dry capsule, usually dehiscent, sometimes indehiscent.
ascending or reflexed, terete to ± flattened, 6–15 × 0.8–1.1 mm, with conspicuous irregular constrictions between seeds, valve margins undulate, all valves free from septum after dehiscence, septum sinuous;
pedicel (2–)3–12 mm.
2–10, ca. 1/2 aborted, arranged± parallel to septum and in alternating pattern between locules, adjacent seeds not overlapping, irregularly well spaced from each, forming a single row in capsule, brown or gray mottled with brown, 1.4–2 × 0.6–0.8 mm, glabrous or puberulent.
few to numerous, without hairs or wings, [very rarely with asymmetrical dry wing (Xylonagra)], or with dry (Oenothera), erose or smooth wing, or with thick, papillate wings (Chylismiella).
= 14.
Gayophytum heterozygum
Onagraceae tribe Onagreae
Gayophytum heterozygum is the only species of Onagraceae outside of Oenothera that is a permanent translocation heterozygote (PTH) (W. L. Wagner et al. 2007), in which the chromosomes form a ring of 14 at meiosis rather than the seven pairs characteristic of all other self-pollinating diploid species of the genus. As is true for other PTH species, G. heterozygum produces only about fifty percent fertile pollen and a correspondingly reduced number of fertile seeds. All other species have less than ten percent of the pollen sterile.
It is not clear whether one or two species were involved in the parentage of Gayophytum heterozygum (H. Lewis and J. Szweykowski 1964; L. B. Thien 1969). This species is morphologically intermediate between G. eriospermum and G. oligospermum and has been suggested by Lewis and Szweykowski to be a PTH species derived by hybridization between them, much like the PTH species in 17. Oenothera.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genera 13, species 265 (12 genera, 199 species in the flora).
Onagreae account for more than half the total genera in Onagraceae and diversified from a center in southwestern North America (L. Katinas et al. 2004). Delimitation of the tribe by W. L. Wagner et al. (2007) differs from previous ones by the exclusion of Gongylocarpus, now in its own tribe, by the segregation of eight genera (Camissoniopsis, Chylismia, Chylismiella, Eremothera, Eulobus, Neoholmgrenia, Taraxia, and Tetrapteron) from Camissonia, and by the inclusion of three previously separate genera (Calylophus, Gaura, and Stenosiphon) in Oenothera. Within the branch of the family that lacks stipules (Gongylocarpeae, Epilobieae, and Onagreae), the last two tribes form a clade that has very strong molecular support (R. A. Levin et al. 2003, 2004), but no obvious morphological synapomorphy. The clade may be defined by a cytogenetic change from the base chromosome number of x = 11 found in Circaeeae, Gongylocarpeae, and Lopezieae, to x = 18 in Epilobieae, and x = 7 in Onagreae; however, these changes could also have occurred independently. Other than the new chromosome number x = 7, the only apparent morphological synapomorphy for Onagreae alone is pollen with prominent apertural protrusions (J. Praglowski et al. 1987, 1989), a character state also found in Circaeeae (Praglowski et al. 1994). The monophyly of Onagreae has moderate (Levin et al. 2004) to strong support (V. S. Ford and L. D. Gottlieb 2007).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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