Taraxia
Nat. Pflanzenfam. 96[III,7]: 216. 1893.
Herbs, fleshy perennial, acaulescent; with thick or slender, sometimes woody taproot, sometimes branched and then usually producing new rosettes. Leaves in a basal rosette; stipules absent; petiolate; blade margins subentire to deeply sinuate or pinnatifid. Inflorescences solitary flowers in leaf axils. Flowers bisexual, actinomorphic, buds erect; floral tube deciduous (with sepals, petals, and stamens) after anthesis, with fleshy basal nectary; sepals 4, reflexed separately; petals 4, usually yellow, rarely white, without spots, usually fading orange, strongly ultraviolet reflective, or sometimes not reflective near base; stamens 8, in 2 unequal series, anthers basifixed, pollen shed singly; ovary 4-locular, with a long, slender, sterile apical projection proximal to opening of floral tube, projection without visible abscission lines at its junctures with floral tube or fertile part of ovary, stigma entire or irregularly lobed, globose, surface unknown, probably wet and non-papillate. Fruit a capsule, straight or slightly irregularly curved, subterete to 4-angled, cylindric-lanceoloid or -ovoid, or oblong-ellipsoid, irregularly loculicidal, gradually tapering into a slender, sterile portion (4–)15–180 mm, sometimes persistent 1+ years, often blackened, thin- or thick-walled; subsessile. Seeds numerous, in 2 rows per locule, pitted or coarsely papillose. x = 7.
Distribution
w North America.
Discussion
Species 4 (4 in the flora).
Taraxia is known from the western United States and southwestern Canada in open, moist clay or sandy sites, usually at low to middle elevations. Taraxia is characterized by its acaulescent habit, seeds in two rows per locule in unwinged, irregularly dehiscent capsules, and notably by having a relatively long, slender, sterile projection at the apex of the ovary that persists on the mature capsule after the floral tube and perianth detach.
This distinctive group of species has been treated variously as a subgenus or section of Oenothera (J. Torrey and A. Gray 1838–1843, vol. 1; P. A. Munz 1965), as a section of Camissonia (P. H. Raven 1969), or as a separate genus (J. K. Small 1896). Traditionally, the two acaulescent annual species now viewed as composing the genus Tetrapteron, which share with Taraxia a sterile apical projection on the ovary, have been included in this group (R. Raimann 1893; Raven 1969). Munz (1965) included the six species in his Oenothera subg. Heterostemon, but separated the four perennials (as sect. Heterostemon) from the two annuals (as sect. Tetrapteron). On the basis of additional information, W. L. Wagner et al. (2007) recognized the two annual species as the genus Tetrapteron. R. A. Levin et al. (2004) found strong molecular support for Taraxia on a weakly supported branch sister to Clarkia + Gayophytum + Chylismiella, whereas the two annual species are strongly monophyletic on a weakly supported branch with Camissoniopsis and Neoholmgrenia. Even though the molecular support for the clade of Clarkia + Gayophytum + Chylismiella + Taraxia is weak, this group of genera shares the feature of basifixed anthers, unlike the versatile anthers of all other genera of tribe Onagreae. P. H. Raven (1964) first pointed out that the basifixed anthers in Taraxia are similar to those found in Clarkia. Species of Taraxia are sometimes grown as ornamentals in rock gardens. Reproductive features include: self-incompatible, flowers diurnal, outcrossing, and pollinated by small bees [T. ovata (E. G. Linsley et al. 1973), T. tanacetifolia (Linsley et al. 1963b)] or facultatively autogamous [T. breviflora, T. subacaulis (Raven 1969)].
Selected References
None.
Key
| 1 | Leaf blade margins usually subentire to sinuate or crisped, sometimes irregularly sinuate-lobed toward base, rarely pinnatifid; herbs sparsely to densely short-hirsute or strigillose, especially on leaf blade margins and ± veins. | > 2 |
| 2 | Leaf blades usually densely short-hirsute on margins and ± veins, sometimes sparsely so; capsules subterete, walls much distended by seeds. | Taraxia ovata |
| 2 | Leaf blades glabrate, veins and margins rarely sparsely strigillose; capsules 4-angled, walls nearly flat, not noticeably distended by seeds. | Taraxia subacaulis |
| 1 | Leaf blade margins pinnatifid; herbs usually sparsely to densely strigillose or short-hirtellous, hairs spreading or appressed. | > 3 |
| 3 | Styles 9.5–20(–25) mm; stigmas exserted beyond anthers at anthesis; petals (8–)10–23 mm; herbs densely or, sometimes, sparsely short-hirtellous and/or strigillose. | Taraxia tanacetifolia |
| 3 | Styles 3–6.5 mm; stigmas surrounded by anthers at anthesis; petals 5–7(–9) mm; herbs densely to sparsely strigillose, sometimes also appressed-hirtellous, hairs spreading or appressed. | Taraxia breviflora |