Flora of North America species comparison

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Genera 22, species 664 (17 genera, 277 species in the flora).

Members of the Onagraceae are especially richly represented in North America. The family comprises annual and perennial herbs, with some shrubs and a few small to medium-sized trees. Most species occur in open habitats, ranging from dry to wet, with a few species of Ludwigia aquatic, from the tropics to the deserts of western North America, temperate forests, and arctic tundra; some species of Epilobium, Ludwigia, and Oenothera can be weeds in disturbed habitats. Members of the family are characterized by 4-merous flowers (sometimes 2-, 5-, or 7-merous), an inferior ovary, a floral tube in most species, stamens usually two times as many as sepals, and pollen connected by viscin threads. Flowers are usually bisexual, sometimes unisexual, and plants are gynodioecious, matinal, diurnal, or vespertine, self-compatible or self-incompatible, often outcrossing and then pollinated by a wide variety of insects or birds, or autogamous (P. H. Raven 1979; W. L. Wagner et al. 2007).

Onagraceae are known in considerable systematic detail, and information is available on comparative breeding systems and pollination biology, on chromosome numbers and cytogenetic relations, often involving translocations, and on vegetative, floral, and seed anatomy, palynology, and embryology. The phylogeny of the family is known in reasonably good detail, with most parts of the trees generally well-supported.

The suprageneric and generic classification presented by W. L. Wagner et al. (2007) differs in a number of ways from the previous classification (P. H. Raven 1979, 1988). Onagraceae are divided into two subfamilies based on a fundamental basal split recognized in all phylogenetic studies (R. H. Eyde 1981; P. C. Hoch et al. 1993; R. A. Levin et al. 2003, 2004; V. S. Ford and L. D. Gottlieb 2007), with Ludwigia on one branch (as Ludwigioideae), and the rest of the family on a second branch (as Onagroideae). Onagroideae are subdivided into six tribes: Circaeeae (including Fuchsieae), Epilobieae, Gongylocarpeae, Hauyeae, Lopezieae, and Onagreae. The Epilobieae and Onagreae are diverse; together they constitute fully two-thirds of the species in the family and include 15 of the 22 genera. The classification following Wagner et al. can be viewed on the Onagraceae web site by Wagner and Hoch at http://botany.si.edu/Onagraceae.

(Discussion copyrighted by Flora of North America; reprinted with permission.)