Key to species and hybrids of Ludwigia with erect, pubescent stems, alternate leaves, 4 sepals, 0 petals, and +/- sessile capsules ca. 1-1.5x as long as broad*

1. Sepals white, sometimes tinged with pink (especially in age); seed surface cells overwhelmingly isodiametric...2.

2. Flowers sometimes clustered at branch tips, but usually also copious throughout in the axils of well developed leaves; leaf bases cuneate...L. pilosa (Hairy Seedbox)

2'. Flowers borne in compact, head-like or spike-like inflorescences, these lacking well-developed leaves; leaf bases narrowly to broadly rounded ...L. suffruticosa (Shrubby Seedbox)

1'. Sepals green or yellowish-green; seed surface cells overwhelmingly elongate (L. ravenii, L. sphaerocarpa) or overwhelmingly isodiametric (L. x simulata) or a robust mix of the two cell types (L. pilosa x sphaerocarpa)...3.

3. Stems and capsules strigillose; seed surface cells elongate in a robust mix of cells transverse and parallel to the long axis of the seed...L. sphaerocarpa (Globe-fruited Seedbox)

3'. Stems and capsules hirtellous (pubescence spreading); seed surface cells various, but not as above...4.

4. Capsules sharply angular; seed surface cells isodiametric...L. x simulata (L. pilosa x L. lanceolata)

4'. Capsules rounded or if weakly angled then not sharply so; seed surface cells elongate or a robust mix of the two cell types...5.

5. Capsules strongly rounded; plants typically robust (1 m and taller), usually of wet sites with long periods of standing water; seed surface cells a robust mix of elongate and isodiametric...L. pilosa x sphaerocarpa

5'. Capsules weakly angled, edges distinctly rounded; plants not particularly robust (usually shorter than 1 m), in periodically moist to wet sites, but not usually in long-standing water; seed surface cells overwhelmingly elongate and transverse to the long axis of the seed...L. ravenii (Raven's Seedbox)

*Key, habitats, distributions, and phenology include data from Peng (1989), Weakley (2015), and Hoch (2021)