Vascular Plants of North Carolina
Account for Yellow Yam - Dioscorea villosa   L.
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Section 5 » Order Liliales » Family Dioscoreaceae
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DistributionThe present map includes all specimens determined as D. "villosa." Many of these will likely be annotated to D. quaternata in the future, especially in the Mountains and Piedmont. The text below refers specifically to taxon "villosa" and not to "quaternata."

RI and NY to MN and KS, south to FL and TX. Apparently mostly in the Coastal Plain.
AbundanceUncommon to infrequent in the Coastal Plain, perhaps frequent in the Sandhills. Possibly absent from the Mountains and Piedmont, but if present, is certainly scarce, as most to nearly all records seem to refer to D. quaternata. NatureServe's Global Rank is only G4G5, as opposed to G5 for D. quaternata. As a result of the Global Rank of G4G5, and the realization that this species (strict sense) is limited in NC mostly to the Sandhills and Coastal Plain, the website editors suggest a rank of S4?, and that might be too liberal at that.
HabitatFloodplains and swamp forests (cypress-gum, maple-gum, etc.), mostly often associated with blackwater systems; blackwater streamheads and ecotones.
PhenologyFlowering late April-June; fruiting September-October.
IdentificationYellow Yam differs from Fourleaf Yam (D. quaternata) in its non-whorled basal leaves (they may be close to each other but are not truly whorled). That other species has whorled basal leaves (usually 4 leaves, but can be 5-7). Also, the entire stem of Fourleaf Yam is smooth vs. pubescent or smooth in Yellow Yam. Gleason (1952) states that fruits of Fourleaf Yam are a bit larger, but gives no measurements. In the field, the leaves and stems of Fourleaf Yam appear glaucescent vs. plain green of Yellow Yam.
Taxonomic CommentsTaxon editors believe that D. quaternata should be split from D. villosa, and NatureServe considers both taxa as good species. See the D. quaternata species account. D. villosa includes D. hirticaulis Bartlett.

Other Common Name(s)Wild Yam. This is the usual name for the species, but with NatureServe and a few other references splitting this taxon back out as a good species, as some older references did, "Wild Yam" is now the name for the combined, broad-sense D. villosa. NatureServe uses Yellow Yam for the common name for its D. villosa.
State RankS5 [S4?]
Global RankG4G5
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