Ludwigia glandulosa Walter subsp. brachycarpa C.-I Peng, 2020

Hoch, Peter C. & Gandhi, Kanchi, 2020, Nomenclatural changes in Onagraceae, PhytoKeys 145, pp. 57-62 : 57

Ludwigia glandulosa Walter subsp. brachycarpa C.-I Peng subsp. nov.

Diagnosis.

Ludwigia glandulosa subsp. brachycarpa differs from typical L. glandulosa in its smaller stature, 10-55(-90) cm (vs. (20-)40-80(-100) cm); narrower leaf blades, 0.3-0.5(-1) cm (vs. 0.3-2.1 cm); shorter sepals, 1.1-1.9 mm (vs. 1.3-2.3 cm); smaller capsules, 2-5 × 1.3-2 mm (vs. (4-)5-8(-9) × 1.6-2(-3) mm); and seed surface cells elongate transversely to length (vs. surface cells elongate parallel to length).

Type material.

USA, Louisiana, Cameron Parish, 3.2 km W of junction State Highways 82 and 27, 29°48.62'N, 93°08.25'W, 1 m, 16 August 1980, C.-I Peng, W. Peng and J. Chen 4367 (holotype: MO 2806683); see fig. 42 in Peng (1989).

Description.

Stems rarely reddish green, 10-55(-90) cm. Leaves: petiole 0-1 cm, blades linear-elliptic to linear, sometimes very narrowly elliptic, those on main axis 3-5(-7) × 0.3-0.5(-1) cm, those on branches 0.8-3.6 × 0.2-0.3(-0.8) cm. Inflorescences: bracteoles attached at base of ovary, 0.4-0.8 × 0.1-0.2 mm. Flowers: sepals 1.1-1.9 × 1-1.8 mm, apex acute or short-acuminate; nectary disc obscurely, minutely papillose; style 0.4-0.8 mm, stigma 0.2-0.3 mm diam. Capsules obscurely 4-angled, 2-5 × 1.3-2 mm, pedicel 0-0.2 mm. Seeds 0.6-0.8 × 0.3-0.4 mm, surface cells elongate transversely to seed length. Chromosome number: n = 16.

Phenology.

Flowering and fruiting April to November.

Etymology.

The subspecific epithet ' brachycarpum ' refers to the short capsules.

Distribution and habitat.

Ludwigia glandulosa subsp. brachycarpa is endemic to the US Gulf Coast from southwestern Louisiana to Nueces County, Texas, and more sporadically northward in eastern Texas to south-central Oklahoma. This distribution is at the extreme southwestern edge of that for subsp. glandulosum , which grows from Texas and Oklahoma east to Virginia and Florida and north to southern Missouri, Illinois, and Indiana ( Peng 1989). Although they overlap in part, the two taxa are only rarely locally sympatric. Ludwigia glandulosa subsp. brachycarpa grows in ditches, low meadows, coastal prairies, seeps in sandy woods, moist sinkholes in granite outcrops, old clay fields at an elevation of 0-200 m.

New combinations

Epilobium L. is the largest genus in the family Onagraceae ; its 165 species are widely distributed in cool or cold regions of the world, with a center of diversity in western North America ( Wagner et al. 2007). A group of annual species with affinities to Epilobium but considered distinct because they lack seed comas was historically segregated as Boisduvalia Spach ( Raven 1976). However, molecular and other evidence ( Hoch and Raven 1992; Baum et al. 1994; Wagner et al. 2007) unequivocally place Boisduvalia within Epilobium as two non-monophyletic sections. Epilobium sect. Epilobiopsis (Spegazzini) Lievens, Hoch & PH Raven is a group of two species characterized by tough, tardily dehiscing capsules, seeds in two rows per locule, and a chromosome number of n = 15; and E. sect. Boisduvalia (Spach) Hoch & P. H. Raven is a group of four species characterized by friable, readily dehiscing capsules, seeds in one row per locule, and chromosome numbers of n = 9, 10, 19. In naming this latter section, however, we overlooked an earlier name at the sectional level, one of two proposed for this group by Fischer and Meyer (1836), who treated the group as part of Oenothera L. due to the absence of seed comas. Therefore, a new combination is required.