This is widespread across eastern and central North America, generally in thin woods on well-drained levees and streambanks, but somwhat conservative and not spreading into adjacent uplands. Variation needs further study. Some less robust southeastern plants, especially in more swampy woods of the lower Mississippi Valley, have distinctly narrower leaf blades (ca. 1.5-3 cm versus 4-6 cm; L/W ca. 3-4 versus 2-2.5), inflorescences with less branching into subverticillate clusters, smaller flowers with more sharply dentate petals, and less conspicuous sepal venation. Such plants have been collected from GRAV (R. Athey 2351 at MO), MARS (R. Athey 4939 at EKY) and adjacent Stewart Co., Tenn. (APSC). They may deserve taxonomic recognition, or perhaps just represent transitions to lanceolata. The potential for fertile hybrids among species of Steironema is well known, though further documentation is needed from the field (Coffey & Jones 1980; F, W). Diploids (2n = 34) predominate in these species, except that ciliata mostly has much higher numbers (2n = 92-112), with diploids reported only from southeastern states. S. ciliata, lanceolata and hybrida form a species-complex with petioles usually ciliate for most of their length, and with erect stems on spreading rhizomes.