1. Amsinckia Lehm.

Plants annual, with slender taproots. Stems erect or ascending, unbranched or branched, pubescent with sparse to moderate, spreading, bristly, pustular-based hairs and usually also sparse to dense, fine, short, more or less appressed, sometimes somewhat matted hairs. Leaves alternate and often also basal, sessile, gradually reduced toward the stem tip. Leaf blades linear to narrowly oblong or oblong-lanceolate, the uppermost sometimes narrowly ovate, narrowed to somewhat rounded at the base, mostly angled to a bluntly or sharply pointed tip, the lowermost leaves tapered at the base and often rounded at the tip, the surfaces and margins moderately to densely pubescent with more or less spreading, bristly, pustular-based hairs. Inflorescences not paired, at first appearing as dense, terminal and apparently axillary (terminal on short axillary branches) clusters, subsequently elongating into ascending, scorpioid, spikelike racemes, occasionally appearing as few-branched panicles, the flowers short-stalked, usually lacking bracts (rarely a few present at the base of the inflorescence). Calyces more or less actinomorphic, 5-lobed nearly to the base, occasionally some of the lobes fused (the calyx then appearing 3- or 4-lobed), the lobes mostly linear to narrowly lanceolate-triangular, with bristly, pustular-based hairs, persistent and ascending at fruiting. Corollas more or less trumpet-shaped, actinomorphic, yellow or orange, sometimes with reddish streaks in the throat, the throat sometimes with small, scalelike appendages, the lobes more or less spreading, rounded. Stamens attached above or less commonly below the midpoint of the corolla tube, the filaments very short, the anthers oblong, not exserted from the corolla. Ovary deeply 4-lobed, the style slender, not exserted from the corolla, often not persistent at fruiting, the stigma capitate, unlobed. Fruits usually dividing into 4 nutlets, these erect, angular-ovoid, attached to the pyramidal gynobase toward the basal portion of a ventral keel, the relatively small scar usually surrounded by a small outgrowth of tissue, the surface appearing variously roughened, warty, or somewhat wrinkled, usually at least in part with small, blunt tubercles, white to grayish white or occasionally tan. Fifteen to 50 species, North America, South America.

The taxonomy of Amsinckia is complex and not well understood, with species boundaries difficult to evaluate because of confusing patterns of morphological variation between populations. Many new species were described by Suksdorf (1931), but the majority of them now seem unworthy of recognition. The nomenclature consequently is confusing, with some species treated under different names in various state floristic manuals. In the present work, the nomenclatural suggestions of Ray and Chisaki (1957) are followed in dealing with these taxa.

In general, Amsinckia species are weedy and are found in open, disturbed sites in a variety of soil types. All the taxa found in Missouri are considered toxic to livestock, especially to horses (Burrows and Tyrl, 2001). Collectors should also exercise caution as the bristly hairs found in abundance on the plants can cause itching and/or dermatitis.