1. Lygodesmia juncea (Pursh) D. Don ex Hook. (skeleton plant)

Pl. 260 g–i; Map 1086

Plants perennial herbs, with deep-set, woody, usually vertical rootstock and branched rhizomes. Latex cream-colored to yellowish white. Stems 1 or few, 10–70 cm long, erect to loosely ascending, sometimes from a spreading base, highly branched, finely longitudinally ridged, glabrous, grayish green. Leaves basal and alternate, sessile, unlobed, entire, glabrous. Basal leaves relatively few, 15–40 mm long, linear or very narrowly lanceolate, withering before the flowers develop. Stem leaves 1–12(–40) mm long, scalelike, linear to very narrowly triangular, mostly withering or shed before the flowers develop. Venation of 1 or 3 main veins, sometimes not apparent. Heads solitary at the branch tips or rarely lateral along the branches, appearing sessile to long-stalked. Involucre 10–16 mm long at flowering, not or only slightly elongating at fruiting, narrowly cylindrical, the bracts in 1 long, inner series and 3 or 4 shorter, outer series, those of the outer series 9–19, variously 1–4 mm long, narrowly triangular, usually purplish-tinged toward the tip, glabrous or sparsely to moderately hairy along the margins; those of the inner series more or less equal, 5–7, narrowly oblong-lanceolate, the margins often thin and pale, the tip appressed-ascending, often purplish-tinged. Receptacle naked but with minute, scaly ridges between the florets. Ligulate florets 4–6. Corollas 12–20 mm long, light lavender, less commonly pink or nearly white. Pappus 6–9 mm long, of numerous apparently smooth (microscopically barbed) bristles, straw-colored to pale tan, persistent at fruiting. Fruits not produced (see discussion below). 2n=18. June–September.

Uncommon, known only from the western portion of the Glaciated Plains Division from Buchanan to Atchison Counties, and from a presumably introduced historical occurrence in St. Louis County (Washington to Nevada and New Mexico east to Minnesota and Texas). Loess hill prairies and loess bluffs; also rarely open, disturbed areas.

Smith (1988) dismissed an Arkansas specimen of this species as representing a nonpersistent chance introduction. A single nonfertile specimen at the University of Missouri herbarium collected on 23 September 1886 by Henry Eggert in St. Louis County (west of Forest Park) also probably documents a waif that failed to persist in some disturbed habitat. Steyermark (1963) excluded this specimen from his map in the belief that it was mislabeled.

Tomb (1980) noted that although L. juncea is widespread, most populations apparently produce few or no viable fruits. This appears to be the case in all of the Missouri specimens examined during the present study. After flowering, the ovary elongates as though the fruit is developing, but at maturity it is abruptly slender and somewhat shrunken below the slightly expanded tip. Tomb (1980) reported that well-formed achenes of L. juncea are 6–10 mm long, cylindrical, obscurely longitudinally lined, and glabrous.

Plants of L. juncea frequently have spherical galls along the stems. These are caused by a small cynipid wasp, Antistrophus pisum Ashmead, whose developing larvae feed on plant tissue inside the galls. The genus Antistrophus utilizes only members of the Asteraceae (Krombein et al., 1979). Apparently, A. pisum has evolved to parasitize only L. juncea and thus requires the skeleton plant to complete its life cycle.

Lygodesmia juncea has a bitter flavor and is thus avoided by livestock. Although there is no evidence that the plants themselves are poisonous, they can accumulate nitrates from the soil in their tissues and thus can become toxic to livestock (Burrows and Tyrl, 2001). Native Americans used the plants medicinally to treat coughs, heartburn, diarrhea, skin problems, kidney problems, and a host of miscellaneous ailments, as well as to increase lactation in nursing mothers (Moerman, 1998).