Trapa bispinosa Roxb. var. iinumae Nakano

Locations ofTrapa bispinosa Roxb. var. iinumae Nakano in Virginia

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Botanical Name
Trapa bispinosa Roxb. var. iinumae Nakano
Common Name
Two-horned Water-Chestnut, Two-horned Trapa
Trapa natans L. var. bispinosa (Roxb.) Makino
Flora of Virginia Name/Status
Trapa bispinosa Roxb.
This species was first discovered in the Potomac River watershed in 1995 and has since been found at nearly 50 sites, many of which are being managed to control its spread. Recently found in Loudoun and Charlotte counties, the latter in the Roanoke River drainage of the southern Piedmont, suggesting that the species is spreading rapidly and likely occuring undetected at additional sites. Similarity to Trapa natans allowed this species to go undetected until fruit differences were discovered and molecular work conducted. This two-horned taxon has been found to be genetically and morphologically most similar to samples of Trapa bispinosa Roxb. var. iinumai from Taiwan (Chorak et al. 2019. Cryptic introduction of water chestunt (Trapa) in the northeastern United States. Aquatic Botany 155: 32-37.) Rybicki (pers. comm.) indicates that all reports of Trapa in our area from the 1950s and earlier are of Trapa natans, but all recent reports are referrable to bispinosa. Recent reports of T. natans in the Digital Atlas may therefore be T. bispinosa.
Artificial ponds and lakes with the exception of an occurrence at Pohick Bay Regional Park.
Native Status

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