Ludwigia sect. Pterocaulon
alternate.
4[or 5]-merous;
petals present, yellow [white];
stamens 2 times as many as sepals;
pollen shed in polyads [rarely tetrads].
oblong-linear to subcylindric, subclavate to oblong-obovoid, or narrowly obpyramidal, prominently 4(or 5)-ribbed or -winged, with thin walls, irregularly dehiscent.
in several rows per locule, free, raphe inconspicuous.
= 16.
Ludwigia sect. Pterocaulon
Species 5 (2 in the flora).
Section Pterocaulon consists of five erect, mainly annual, diploid species (T. P. Ramamoorthy 1979; Ramamoorthy and E. Zardini 1987); three occur only in Argentina, Brazil, Paraguay, and Uruguay. Ludwigia decurrens and L. erecta occur more widely in South America and extend to the southeastern United States, Mexico, and the Caribbean; both also occur in Africa, and L. decurrens is naturalized in Asia and Europe (P. H. Raven 1963[1964]; Ramamoorthy and Zardini). Four species are autogamous, with the remaining one (L. longifolia) self-compatible but primarily outcrossing. Unlike species of sect. Myrtocarpus, in which section these species were treated prior to 1979, all are diploid annuals with mostly winged stems and very narrow, sublinear leaves. Sect. Pterocaulon appears to be polyphyletic in analyses by Liu S. H. et al. (2017), but not all species were sampled, and no change in classification is proposed here.
This section was delimited and named earlier as Diplandra Rafinesque 1840, but that name was pre-occupied by Diplandra Bertero 1830 and Diplandra Hooker & Arnott 1838, name conserved.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
