Vascular Plants of North Carolina
Account for Mexican Primrose-willow - Ludwigia octovalvis   (Jacquin) Raven
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Section 6 » Order Myrtales » Family Onagraceae
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Author(Jacquin) Raven
DistributionA relatively tiny range in the state, essentially only along the Cape Fear River and Brunswick River in the vicinity of Wilmington. Apparently not known farther west in Brunswick County, nor farther to the north either. In 2020 a specimen originally identified as L. hexapetala (Sorrie 11997 NCU) was annotated to L. octovalvis.

This is a species of the Deep South, found sparingly north to extreme southeastern NC, and south to the Gulf Coast, and much farther into the tropics. There is some confusion between this species and the non-native L. bonariensis in the literature. In fact, RAB (1968) had records for L. octovalvis included within L. bonariensis. Note, however, that Wikipedia says "its native distribution is unclear", and there is probably not unanimity that it is native as far north as NC.
AbundanceDespite there being only one general area for this species in the state, it appears to be widespread in this small area on Eagles Island or the adjacent areas. The NCNHP has given a State Rank of S2 and only on its Watch List, as some sites do appear to be disturbed ground. It may well deserve to be moved up to S1 and tracked as Significantly Rare, pending further information on its range and popluations there.
HabitatThis is a species of the extensive tidal freshwater marshes in the Cape Fear/Brunswick River region just west and northwest of Wilmington. It also grows in damp disturbed ground in this area. In Stanly County, it grows in a beaver pond that lies in an old meander of the Pee Dee River.
PhenologyBlooms from May to September, and fruits shortly after flowering.
IdentificationThis is a very tall and robust species, growing as high as 5-6' tall. The stem is generally smooth, much branched, and with alternate leaves. The leaves are variable, but mostly quite narrow, lanceolate to narrowly elliptic, to about 6" long but only 1/2" wide at best. The flowers, in leaf axils, are the largest of the native Ludwigia species, with the 4 bright yellow and rounded petals each about 3/4" long, meaning the spread flower is often about 1.5" across. The floral tubes and capsules are quite long, up to 1" but narrow. Note that the non-native L. bonariensis has been collected in the state a few times, but SERNEC records from the Wilmington area probably are of L. octovalvis. That exotic has much larger yellow flowers, each petal about 1.5" across and a full spread flower about 3" across, and its sepals are about 10 mm (2/5") wide at the base, versus sepals only 3-5 mm (1/6") wide at the base in the native species. This species should be reasonably obvious to biologists in the Cape Fear River area near Wilmington, as it is a conspicuous species of marsh edges owing to its tall size and large yellow 4-petalled flowers.
Taxonomic CommentsAs mentioned above, there has been confusion in NC between this native species and the non-native L .bonariensis. Most or nearly all recent references do have this confusion "sorted out", though the provenance of L. octovalvis as far north as NC might still be unsettled.

Other Common Name(s)Longfruit Primrose-willow
State RankS2? [S2]
Global RankG5
State StatusW1
US Status
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