Chylismia is a genus of flowering herbs in the evening primrose family Onagraceae, comprising 16 species native to the western United States and northwestern Mexico. The genus was originally described as an unranked group within Oenothera by Torrey and A. Gray in 1840, later treated as a section of the broad genus Camissonia, and was formally elevated to genus rank following molecular phylogenetic studies by Levin et al. (2004) and Wagner et al. (2007). Within Onagraceae, Chylismia is strongly supported as sister to the realigned Oenothera, and that combined clade is in turn sister to Eulobus.
Plants in the genus are usually annual herbs, though some species are perennial and a few are biennial. Stems are ascending to erect and typically branched. Leaves are alternate, long-petiolate, and borne both basally and along the stem; many species form a conspicuous basal rosette. Leaf blades are often pinnately or bipinnately lobed, with a large terminal lobe, and the underside characteristically bears scattered, usually brown oil cells. The inflorescence is a raceme that may be erect or nodding. Flowers are bisexual and actinomorphic, with four reflexed sepals, four petals (usually yellow or white, often fading to orange-red, sometimes lavender or purple, and frequently marked with one or more red dots near the base), and typically eight stamens arranged in two subequal series. The floral tube is deciduous and bears a basal nectary. Capsules are straight to slightly curved, subterete to clavate or oblong-cylindrical, borne on distinct pedicels, and open by regular loculicidal dehiscence; seeds are numerous, arranged in two rows per locule, and are lenticular to narrowly ovoid with a finely pitted surface.
Chylismia is distinguished from related genera formerly lumped within Camissonia by its consistently straight to arcuate (never twisted or curled) capsules and by its two-ranked seeds. Most species are diploid (2n = 14), though tetraploids (2n = 28) occur, and floating chromosomal translocations are relatively common in the genus. Pollination biology varies considerably: several species, including C. claviformis and C. brevipes, are self-incompatible and visited by oligolectic bees, while C. cardiophylla is pollinated mainly by small moths and C. arenaria, which produces notably long floral tubes, is visited by hawkmoths.
Etymology
The name Chylismia derives from the Greek chylos (juice or succulence) combined with the suffix -isma (condition), alluding to the fleshy leaves of C. scapoidea, which is the type species of the genus.
Distribution
Chylismia is endemic to western North America, with all 16 species occurring in the western United States and extending into northwestern Mexico. The genus is characteristic of arid and semi-arid habitats in this region.
Ecology
Chylismia species occupy a range of pollination strategies. Several species (C. brevipes, C. claviformis, C. multijuga, C. munzii, and likely others) are self-incompatible and depend on oligolectic bees for pollination, while others are autogamous. C. cardiophylla is pollinated mainly by small moths, and C. arenaria, which produces unusually long floral tubes, is visited by hawkmoths. Flowers in most species open during the day, though some subspecies of C. claviformis open one to two hours before sunset and are visited by both oligolectic bees and moths.
Taxonomy Notes
Chylismia was originally circumscribed as an unranked group within Oenothera by Torrey and A. Gray (1840) and subsequently treated as Camissonia sect. Chylismia by P. H. Raven and as a subgenus and section of Oenothera by other authors. Molecular phylogenetic work by Levin et al. (2004) and Wagner et al. (2007) demonstrated that the group merits recognition as a distinct genus, closely related to the realigned Oenothera and sister to Eulobus. Two sections are currently recognised within Chylismia: sect. Chylismia (floral tubes 0.4–9 mm; pollen shed singly; leaves pinnately lobed; usually annual) and sect. Lignothera (floral tubes 4.5–40 mm; pollen shed in tetrads; leaves unlobed; usually perennial).
