Mapping here is provisional and largely based on annotations of Loconte & Blackwell (1985); Thompson (2008) added MADI to reported counties, and there are several recent records from iNaturalist.org (mapped here as open circles). Some authors have doubted the rationale for distinction of giganteum (Cr, J, RAB). It is reported mostly from central Appalachian to northeastern regions, centered on W.Va. to N.Y., but extending west to Ind. (SERNEC 2024) and overlapping much with thalictroides (FNA 3). Apparent intermediates exist in In. (S. Namestnik, pers. comm.). C. giganteum may reach the southwestern margin of its range in c. Ky. and c. Tenn. (K). Loconte & Blackwell (1985; FNA 3) insisted that giganteum is a species distinct from thalictroides, differing in its larger pistils (3-5 mm long versus 1-3 mm), styles (1-2 mm long versus 0.25-1 mm), stamen filaments (1.5-2.5 mm long versus 0.5-1.5 mm), and sepals (6-9 mm long versus 3-6 mm). Sepals are usually purple, less often red, brown or yellow (versus yellow to greenish-purple). It typically flowers about two weeks earlier (mostly in late Mar to early Apr versus mid- to late Apr), often with the unfolding leaves. It has fewer flowers per inflorescence (4-18 versus 5-70), less divided first leaves (mostly 2- or 3-ternate versus 3- or 4-) but larger leaflets (5-10 cm long versus 3-8 cm). However, there have been very few reported attempts to distinguish these species in surveys of flora or vegetation; the distribution of giganteum in Ky. suggests an association with more acid soils. There are also no reported horticultural comparisons despite much interest in medicinal uses of Caulophyllum. The potent alkaloids and saponins of this genus have been reviewed by Xia et a. (2014).