This is widespread across North America, especially along riparian zones. It is generally rare to absent on infertile acid soils. In Ky., some western material is referable to var. violaceum (Kirchn.) Jaeger (with twigs glabrous, often glaucous), or to var. texanum Pax (with pubescent twigs, leaflets and fruits). However, these taxa are not generally distinguished in eastern states (W). Typical Acer negundo is remarkable for the bright green color of its twigs in the first year or so, then turning orange-brown for another year or two; and the wood has mysterious red staining when wounded (Morse & Blanchette 2002). (The few other deciduous woody plants with persistently green twigs in Ky. include Sassafras, Euonymus and Oxydendrum.) Despite this greenness in negundo, there appears to be relatively little browsing by deer (e.g. Cogger et al. 2014) or even by beaver in some cases (e.g. Nixon & Ely 1969, Barnes & Dibble 1998). Moreover, this tree species can cause "seasonal pasture myopathy" in horses (Wu et al. 2016), apparently due to toxicity from "hypoglycin A" (2-methylene-cyclopropanyl-alanine). A. negundo is also the only North American maple reported to contain a cerebroside (glycosphingolipid based on an amino-alcohol). Such compounds are known to influence nervous tissue (Wu et al. 2016). Twigs and wood of the species have had some traditional emetic use by native Americans, with "a distinct and unpleasant [slightly fetid] scent when wet, which mostly subsides once dry" (wood-database.com; and pers. obs.); but this smell has not yet been linked to a particular chemical. A. negundo is strictly dioecious, but there is much variation in sex ratio. Studies in Utah reported male:female ratios averaging about 2:3 in streamsides and 2:1 outside streamsides; males had more conservative use of water and other physiological differences, including faster growth rates in drier conditions but slower in wet, and reduced defenses against herbivores (e.g. Jing & Coley 1990, Ward et al. 2002). In Michigan, males tended to outnumber females and produced more foliage mass, but females produced more wood (Ramp & Stephenon 1988). As in other species of Acer: "The samaras often develop parthenocarpically; in dioecious taxa this is always the case" (de Jong 1976).