Vascular Plants of North Carolina
Account for Water Stargrass - Heteranthera dubia   (Jacquin) MacMillan
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Section 5 » Order Liliales » Family Pontederiaceae
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Author(Jacquin) MacMillan
DistributionKnown (collected) only from a single site in the state -- in the New River in Alleghany County. Despite it having been collected from at least 35 VA counties, many in the southern Piedmont (not to mention mountains), the fact that it barely enters the edge of NC is quite striking.

This is a very widespread species, occurring across much of southern Canada and southward to western FL and CA. However, within this huge range it is very scarce south of VA and MO.
AbundanceThis website considers it of historical occurrence in NC. The NCNHP's State Rank and State Status are puzzling and incorrect. As it has apparently not been found in the state since its discovery in 1961, the Rank should be SH and not S1?. In addition, W3 implies poor documentation, such as a sight report or a specimen that cannot be located. The SERNEC database lists five NC collections, all duplicates of one gathering. Thus, the species is clearly rare enough for state listing, and as it is of historical occurrence, that status should either be SR-P (Significantly Rare - Peripheral) or SC-H (Special Concern - Historical). The website opts to be conservative and proposes Signficantly Rare.
HabitatThis species grows in mostly sluggish water, in a swampy margin of a river in NC; elsewhere also in lakes and ponds. Weakley (2018) mentions it prefers calcareous substrates in its range, but such aquatic sites are extremely rare in NC (discounting limesink ponds in the lower Coastal Plain).
PhenologyBlooms from late July into October, and fruits shortly after blooming.
IdentificationThis is a very odd flowering plant. There are a number of vascular plants that grow submerged in fresh water in NC, and most of these have linear to filamenous leaves, as this one does. However, most have tiny or basically invisible flowers, such as Myriophyllum species, Proserpinaca species, and Hornleaf Riverweed (Podostemum ceratophyllum). Yet, Water Stargrass has a conspicuous bright yellow 6-pointed star-like flower (6 very narrow tepals) on the water surface that makes it look like no other species when in bloom. These flowers are about 1/2-inch across, not at all a large flower, but one that catches attention on a water surface. Actually, the plant looks a bit like submerged green Spanish-moss (Tillandsia usneoides), which also has a surprisingly "sizable" flower! As it has been found in many southwestern VA counties close to NC, it certainly could be re-found in the northwestern corner of the state, either in the Piedmont or in the mountains.
Taxonomic CommentsNone

Other Common Name(s)Grassleaf Mud-plantain
State RankS1? [SH]
Global RankG5
State StatusW3 [SR]
US Status
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