Bitterweed [Greek tetra, four, and neuron, nerve, alluding to venation of ray floret corollas]

Mark W. Bierner, Billie L. Turner

Annuals or perennials, 2–50+ cm (perennials with ± branched, woody caudices). Stems 1–60, erect or ± decumbent, unbranched or sparingly branched distally. Leaves all basal, or basal-proximal, or basal and cauline; alternate; petiolate or sessile; blades (usually with distinct midribs) mostly oblanceolate to linear or filiform, sometimes lobed, ultimate margins usually entire, sometimes toothed, faces glabrous or ± hairy, eglandular or ± gland-dotted. Heads radiate or discoid, borne singly or in paniculiform to corymbiform or fastigiate arrays. Involucres hemispheric to campanulate 6–20 mm diam. Phyllaries 11–60+ in 3 series (mostly spreading to erect in fruit, distinct, herbaceous; outer with or without scarious margins, abaxial faces ± hairy; mid usually same number as, alternating with, and similar to outer, almost always with ± scarious margins; inner narrower than others, margins scarious). Receptacles hemispheric to conic, shallowly pitted or smooth, epaleate. Ray florets 0 or 7–27, pistillate, fertile; corollas (usually marcescent) yellow (laminae fan-shaped to oblanceolate, usually 3-lobed). Disc florets 20–250+, bisexual, fertile; corollas yellow proximally, yellow or purplish distally, tubes shorter than cylindric to cylindro-campanulate throats, lobes 5, ± deltate. Cypselae ± obpyramidal, moderately to densely hairy; pappi persistent, of 4–8 usually aristate, scales. x = 15.

Species 9 (9 in the flora): North America, Mexico.

Here, strigoso-canescent refers to often silvery induments (hairs tightly appressed, relatively short, 1–1.5 mm) of Tetraneuris argentea and T. acaulis var. acaulis. Such induments contrast with lanuginose or sericeous induments (hairs spreading, ca 1.5–3 mm) in other taxa, including T. ivesiana and the other three varieties of T. acaulis.

SELECTED REFERENCES

Bierner, M. W. and R. K. Jansen. 1998. Systematic implications of DNA restriction site variation in Hymenoxys and Tetraneuris (Asteraceae, Helenieae, Gaillardiinae). Lundellia 1: 17–26. Bierner, M. W. and B. L. Turner. 2003. Taxonomy of Tetraneuris (Asteraceae: Helenieae: Tetraneurinae). Lundellia 6: 44–96. Greene, E. L. 1898. Studies in the Compositae—VII. 1. Some helenioid genera. Tetraneuris. Pittonia 3: 264–270. Rydberg, P. A. 1915b. Tetraneuris. In: N. L. Britton et al., eds. 1905+. North American Flora.... 47+ vols. New York. Vol. 34, 100–108.