1b. var. serotina (Greene) Rehder

Schmaltzia serotina Greene

R. canadensis var. serotina (Greene) E.J. Palmer & Steyerm.

R. trilobata var. serotina (Greene) F.A. Barkley

Mature leaflets 2.0–7.5 cm long, 3–7 cm wide, sessile, sparsely pubescent with appressed, silky hairs above and below. Terminal leaflet largest, broadly obovate, variously lobed above, rounded, blunt to occasionally acute. Flowering at or after expansion of the leaves. Bracts reddish brown, densely woolly at the base and along the margins. Flower stalks 2–3 mm long, densely woolly to nearly glabrous. Sepals 1.0–1.2 mm long, about 1 mm wide. Petals 2.2–2.4 mm long, usually hairy on the inner surface. Fruits 5–6 mm wide, often somewhat shiny. Late April–early May.

Scattered south of the Missouri River, uncommon northward to Monroe and Pike Counties, apparently absent from the Mississippi Lowlands Division (Illinois to South Dakota and Texas). Glades, tops of bluffs, and openings of mesic to dry upland forests.

The native range of this variety in Missouri has become obscured as a result of its use for wildlife plantings in woodland restorations and other places managed for natural features.

The var. serotina is a variable taxon but is distinguished from var. aromatica by several characters. In Missouri, var. serotina flowers later than var. aromatica, after the leaves have made their appearance. The name serotina refers to this later flowering. Spellman and Dunn (1965) recorded phenological data on populations for four years and found that the peak of flowering was consistently three weeks apart. The stems in var. serotina tend to be more branched and twisted, as in R. trilobata. The mature leaves are about the same size as in var. aromatica, but the terminal leaflet has a tendency to be 3-lobed, as in R. trilobata, and the teeth are more irregularly spaced and rounded. In addition, the flower stalks of var. serotina are usually somewhat longer than in var. aromatica, and the petals are usually hairy on the inner surface. Although var. serotina is distinct in Missouri and Arkansas, populations in Oklahoma and Kansas grade into R. trilobata, which is the common species in the Great Plains and western North America. Indeed, Spellman and Dunn (1965) agreed with Barkley (1937) that var. serotina had more in common with R. trilobata than with R. aromatica. They pointed out that var. serotina often occurs in more xeric situations, such as rocky outcrops and steep bluffs, much like R. trilobata does farther west.

This taxon originally was described as a distinct species, Schmaltzia serotina, with the type specimen from Independence (Jackson County). Since then, various botanists have treated it as a variety of the eastern R. aromatica, then called R. canadensis (now considered a synonym of R. aromatica), and the western R. trilobata. Some authors have gone further and treated R. trilobata as a variety of R. aromatica (McGregor, 1986c). However, R. trilobata appears to be a distinct and more or less uniform species, at least throughout much of the central Great Plains region, with small- to medium-sized 3-lobed leaflets. Some populations of R. trilobata flower before the leaves emerge, and some after the leaves emerge. Further complications arise from the fact that several varieties of R. trilobata have been described for the southwestern United States and California, which are in need of further study. Perhaps all these taxa eventually will be treated as varieties of a single widespread, polymorphic species.