4. Lobelia siphilitica L. (blue cardinal flower, great lobelia, blue lobelia)

L. siphilitica var. ludoviciana A. DC.

Pl. 331 i, j; Map 1411

Plants perennial herbs with fibrous roots. Stems (10–)30–100(–150) cm long, erect or strongly ascending, unbranched or less commonly few-branched toward the tip, often slightly winged, glabrous or sparsely pubescent with short, loosely ascending hairs. Leaves sessile or short-petiolate, gradually reduced from about the stem midpoint to the stem tip. Leaf blades 2–15 cm long, 0.5–6.0 cm wide, lanceolate to elliptic, narrowly oblong, or oblanceolate, angled or tapered at the base (those of the uppermost leaves sometimes more or less rounded), the base usually somewhat decurrent below the attachment point as a pair of narrow wings of green tissue along the stem, rounded or more commonly angled or tapered to a bluntly or sharply pointed tip, the margins finely and bluntly to sharply toothed, the surfaces glabrous or less commonly the undersurface with sparse, short hairs or minutely roughened along the veins. Inflorescences dense racemes (the flower stalks mostly 3–9 mm long), the bracts of the lower flowers more or less leaflike, the upper bracts gradually reduced (each flower also with a pair of minute bracts immediately below or farther below the calyx). Calyces 8–18 mm long, the tube 2–4 mm long at flowering, becoming somewhat enlarged as the fruit matures, the slender lobes 6–14 mm long, becoming somewhat elongated as the fruit matures, with relatively long, conspicuous auricles. Corollas 16–32 mm long, blue to bluish purple, sometimes with white, longitudinal striping, rarely completely white, the outer surface glabrous or with short, spreading hairs along the veins, the tube 11–20 mm long, with slitlike openings (fenestrate), the lobes 5–12 mm long. Filament tube 12–15 mm long, blue, the anther tube 3–5 mm long. Fruits 5–9 mm long. Seeds 0.6–0.8 mm long, ellipsoid, the surface with a series of minute pits and ridges, yellowish brown. 2n=14. August–October.

Scattered nearly throughout the state (eastern U.S. west to North Dakota, Wyoming, and Texas; Canada). Banks of streams, rivers, and spring branches, margins of ponds and lakes, bottomland forests, moist depressions of upland prairies, sloughs, swamps, fens, and moist ledges of bluffs; also pastures, ditches, and roadsides.

Two varieties of L. siphilitica were recognized by McVaugh (1936) and were included for Missouri by Steyermark (1963). Lobelia siphilitica var. siphilitica is the typical form of the species east of the Mississippi River, with hairy, relatively broad leaves 2–6 cm wide, a densely flowered inflorescence, and hairy calyces and flower stalks. Lobelia siphilitica var. ludoviciana is more common west of the Mississippi River and is said to be smaller, with glabrous leaves mostly less than 2 cm wide, a more sparsely flowered inflorescence, and glabrous calyces and flower stalks. Although these varieties may be distinguishable in other states, almost all the Missouri material lies somewhere in between these extremes. Plants with entirely white corollas have been called f. albiflora Britton.

Lobelia siphilitica and L. cardinalis are closely related. Ordinarily, the two species are isolated by differences in floral morphology and pollinator preferences, but occasional natural hybrids are produced. In Missouri, hybrids have been collected most often along the Current, Jacks Fork, and Eleven Point Rivers. The hybrids are intermediate between the parents for most characters, and they usually have distinctive reddish purple or less commonly somewhat blue-, purple-, and white-variegated corollas. They are uncommon and apparently sterile (Bowden, 1982). Such plants were first reported from Missouri by Steyermark (1952, 1963) and rediscovered by Witherspoon (1974). The correct name for these hybrids is Lobelia Hspeciosa Sweet, although Steyermark (1963) referred to them by the incorrect name L. Hsiphilitica var. hybrida Hook.