Herbs, annual, caulescent; taproot simple or branched. Stems usually delicate, erect or spreading, densely branched or unbranched, epidermis usually exfoliating near base. Leaves cauline, usually alternate, sometimes subopposite proximally; stipules absent; sessile or petiolate; blade margins entire. Inflorescences panicles or racemes, erect, usually flowering at distal nodes only, sometimes from basal nodes. Flowers bisexual, actinomorphic, buds erect; floral tube inconspicuous, deciduous (with sepals, petals, and stamens) after anthesis, nectary unknown, presumably basal; sepals 4, reflexed singly or in pairs; petals 4, white with 1 or 2 yellow or greenish yellow areas at base, fading pink or red; stamens 8, in 2 unequal series; anthers ± basifixed, pollen shed singly; ovary 2-locular; stigma entire, subglobose to hemispheric, surface wet and non-papillate. Fruit a capsule, straight or slightly curved, flattened or subterete and often constricted between seeds, loculicidally dehiscent, valves all free or 2 free and 2 remaining attached to septum after dehiscence; usually pedicellate. Seeds 4–50+, in 1 row per locule, ovoid. x = 7.

Distribution

w North America, nw Mexico, w South America.

Discussion

Species 9 (8 in the flora).

Gayophytum consists of nine annual species that usually occur in gravelly or sandy soil in open coniferous forests, among sagebrush, at the drying edges of meadows, or along roadsides at 100–4200 m. Six species are diploid (n = 7) and three are tetraploid (n = 14, G. diffusum, G. micranthum, and G. racemosum). Seven species occur exclusively in western North America, with some species reaching Baja California, Mexico, or southern Canada; two species are endemic to California (G. oligospermum in the Transverse and Peninsular ranges of southern California, and G. eriospermum in the central and southern Sierra Nevada). One species, G. micranthum Hooker & Arnott, is endemic to southern South America in Argentina and Chile, and one species, G. humile, occurs on both continents, with a wide distribution in the western United States and a limited one in Argentina and Chile. Two or more species are often found growing together.

Reproductive features include: self-compatible; flowers diurnal, fading mid day; floating chromosomal reciprocal translocations in at least one species (Gayophytum eriospermum), and one species (G. heterozygum) is a permanent translocation heterozygote (PTH); most species are autogamous (or even cleistogamous); some species with larger flowers and the stigma elevated above the anthers are outcrossing and pollinated by syrphid flies or bees.

Gayophytum is the only genus in Onagreae that has a 2-locular capsule with one row of seeds in each locule. In addition, seeds maturing in the capsules exhibit a variety of arrangements that are useful in the taxonomy of the genus. The terminology that has been used in describing these patterns has been somewhat confusing. The seed arrangement patterns are described here so that minimal and directly comparable terminology can be used in the key and descriptions. In the basic arrangement the septum is straight and the seeds in each locule are arranged obliquely to the septum and subopposite to seeds in the adjacent locule, forming two even rows in the capsule. This condition occurs in two species (G. humile, G. racemosum). In these species the capsule walls are smooth and flat or slightly constricted between the seeds. The remaining species have seeds arranged more or less parallel to the septum, and have either a straight septum or a somewhat to strongly sinuous septum. In G. decipiens the septum is straight and the seeds are in two subopposite rows with the capsule walls smooth and flat or slightly constricted between the seeds. All of the remaining species have a somewhat to strongly sinuous septum with the seeds arranged in an alternating pattern between the locules, and the adjacent seeds are either strongly or slightly overlapping or sometimes not overlapping and well spaced from each other. In these species the capsules walls are somewhat to strongly constricted between the seeds giving a torulose appearance to the capsule, sometimes described in the literature as lumpy, especially in the most extreme case in the capsules of the PTH G. heterozygum where roughly half of the seeds abort before maturity giving a very irregular, lumpy appearance to the capsule. In two of these species (G. ramosissimum and some populations of G. diffusum subsp. parviflorum) the seeds are crowded and strongly overlapping, so much so that they appear to form two irregular rows in each locule. In all other species with alternate seeds there is no or little overlap and overall they form a single row in the capsule.

Selected References

None.

Lower Taxa

Gayophytum decipiens, Gayophytum diffusum, Gayophytum eriospermum, Gayophytum heterozygum, Gayophytum humile, Gayophytum oligospermum, Gayophytum racemosum, Gayophytum ramosissimum

Key

1	Petals 3–8 mm; sepals 2–6 mm; stigmas usually exserted beyond anthers of longer stamens at anthesis.	> 2
1	Petals 0.5–3 mm; sepals 0.4–2 mm; stigmas surrounded by anthers at anthesis.	> 3
2	Petals 4–8 mm; sepals 3–6 mm; seeds 1.2–2.3 mm; Sierra Nevada and Greenhorn mountains, California.	Gayophytum eriospermum
2	Petals 3–5(–7) mm; sepals 2–3(–5) mm; seeds 1–1.6 mm; widely distributed in w United States but absent from Sierra Nevada and Greenhorn mountains.	Gayophytum diffusum
3	Capsules flattened, not constricted between seeds; stems usually branched only near base, secondary branches few or none; seeds 0.7–1.1 mm, arranged obliquely to septum, subopposite to seeds in adjacent locule forming 2 even rows.	> 4
3	Capsules terete to ± flattened, somewhat to conspicuously constricted between seeds; stems branched only distally or throughout, secondary branches usually many; seeds (0.8–)1–2 mm, arranged ± parallel to septum, and either subopposite forming 2 even rows with a straight septum, or arranged in alternating pattern with sinuous septum.	> 5
4	Two valves of capsule remaining attached to septum after dehiscence; pedicels 0–0.5 mm; seeds 24–50 per capsule.	Gayophytum humile
4	All valves of capsule free from septum after dehiscence; pedicels 0.4–2 mm; seeds (10–)14–34 per capsule.	Gayophytum racemosum
5	Seeds ca. 1/2 aborted (pollen ca. 50% fertile); capsules with conspicuous irregular constrictions between seeds (due to aborted seeds).	Gayophytum heterozygum
5	Seeds all developing (pollen 90–100% fertile); capsules with somewhat to conspicuous irregular constrictions between seeds.	> 6
6	Seeds in each locule crowded and overlapping.	> 7
6	Seeds in each locule not crowded and overlapping.	> 8
7	Petals 0.7–1.2(–1.5) mm; pedicels longer than capsules, (3–)5–12 mm; seeds 10–30 per capsule.	Gayophytum ramosissimum
7	Petals 1.2–3 mm; pedicels usually shorter than capsules, 2–10(–15) mm; seeds (3–)6–18 per capsule.	Gayophytum diffusum
8	Seeds mostly more than 9 per capsule, subopposite or alternate; capsules with inconspicuous constrictions between seeds, septum nearly straight.	> 9
8	Seeds mostly 9 or fewer per capsule, usually alternate; capsules with conspicuous constrictions between seeds, septum sinuous.	> 10
9	Stems branched throughout, usually with 2–8 nodes between branches; petals 1.1–1.8 mm; petioles 0–5 mm.	Gayophytum decipiens
9	Stems branched or unbranched at base, much branched distally, usually with 1 or 2 nodes between branches; petals 1.2–3 mm; petioles 0–10 mm.	Gayophytum diffusum
10	Seeds (1–)3–5 per capsule; pedicels about equal to capsules, 3–11 mm; s California.	Gayophytum oligospermum
10	Seeds (3–)6–18 per capsule; pedicels usually shorter than capsules, 2–10(–15) mm; widely distributed, British Columbia, w United States.	Gayophytum diffusum