4. Malva pusilla Sm. (dwarf mallow)

Pl. 454 j, k; Map 2059

Plants annual or perennial. Stems 15–100 cm long, spreading to ascending, sparsely pubescent with simple and stellate hairs. Stipules 3–5 mm long, narrowly triangular to ovate-triangular. Leaf blades 1–5 cm long, flat or slightly crisped along the margins, circular to broadly kidney-shaped in outline, unlobed or broadly and very shallowly 5-lobed (much less than 1/2 way to the base), the margins finely scalloped or toothed, the surfaces glabrous or sparsely pubescent with mostly fasciculate and stellate hairs, especially at the base. Flowers in axillary clusters, short- to long-stalked at flowering, the stalk elongating as the fruits develop, the bractlets subtending the calyx linear, with simple and fasciculate hairs along the margins. Calyces 3–5 mm long at flowering, initially cup-shaped, not or only slightly enlarged and flattened horizontally at fruiting, at least the lobes remaining green, herbaceous, and without a distinct network of veins, the outer surface pubescent with mostly simple and fasciculate hairs, the marginal hairs 0.6–1.2 mm long (mostly more than 1 mm long). Petals 0.3–0.5 cm long, slightly shorter than to slightly longer than the calyx, white, light pink, or pale lavender. Fruits 1.5–2.0 mm long, the dorsal surface flat, glabrous or finely stellate-hairy, strongly transversely wrinkled, and with a reticulate pattern of thickenings, the junction between the dorsal and lateral surfaces narrowly angled and sometimes appearing toothed (but generally not noticeably winged), the sides thin and papery, with a radiating network of thickened veins. Seeds 1.0–1.5 mm long. 2n=42. May–October.

Introduced, uncommon and widely scattered in Missouri (native of Europe, sporadically naturalized in the U.S.).

At one time, the name M. rotundifolia L. was routinely applied to plants presently known as either M. neglecta or M. pusilla in the botanical literature (Voss, 1985; Turland, 1996a), resulting in confusion as to correct application of that name and many misdetermined herbarium specimens. This was the case in Missouri, where M. pusilla is less common than reported in the earlier literature (Palmer and Steyermark, 1935). Turland (1996a) proposed that the name M. rotundifolia should be rejected officially as an ambiguous name, and his proposal subsequently was approved at the 1999 International Botanical Congress.

The character of whether the margin between the dorsal and lateral surfaces of the mericarps is merely angled or narrowly winged, which has been used by some authors (Steyermark, 1963) to distinguish M. pusilla from M. parviflora, is very difficult to interpret. In spite of the seemingly easily observed key characters, some specimens can be difficult to discriminate among M. neglecta, M. parviflora, and M. pusilla.