Danaea, Smith, 1793

Christenhusz, Maarten J. M., 2024, A new species of the fern genus Danaea (Marattiaceae) in the Greater Antilles, Phytotaxa 650 (3), pp. 291-296 : 294-295

Key to the species of Danaea in the Greater Antilles

Notes:—In various cases herbarium material may be difficult to identify, because characters like the rhizome position, habit and positioning of the leaves are not preserved. I have attempted an identification key, but admit that some species are difficult to diagnose based on herbarium material.

Danaea × jamaicensis Underwood (1902: 675) appears to be a hybrid between D. mazeana Underwood (1902: 676) and D. jenmanii Underwood (1902: 677) in places where both species occur together, most frequently in Hardwar Gap, Jamaica (e.g. coll. Christenhusz 3372 IJ, TUR). This will key out as D. mazeana but occasionally will have apical buds like D. jenmanii . It is intermediate between these species in most characters.

Danaea geniculata Raddi (1819: 281) is a species complex which will require a population genetics approach across its broad Neotropical range to sort out the species boundaries. Danaea arbuscula Christenhusz & Tuomisto (2006: 18) and D. ulei Christ (1905: 368) also belong to this complex, and may be undescribed taxa on Puerto Rico, because these species were described from South America and therefore will have been geographically separated for a long time. Molecular studies using SNPs and coalescent methods ( Baird et al. 2008, Bryant et al. 2012) to examine possible genetic clusters with NGS admix ( Skotte et al. 2013) will be needed to resolve these and other species complexes in Danaea .

1. Pinna margins dentate, denticulate, serrate, serrulate or crenulate at apices.....................................................................................2.

1. Pinna margins entire, sometimes slightly sinuate at apices...............................................................................................................6.

2. Rhizomes dorsiventral; petioles without nodes; blades abrupt at the base, without reduced pinnae protruding from the lowest nodes............................................................................................................................................................. Danaea nodosa (L.) Sm.

2. Rhizomes dorsiventral or radial; petioles with (0–) 1–4 nodes, when nodes absent, then blades gradually tapering towards reduced, small, almost rotund pinnae at the blade bases..................................................................................................................................3.

4. Terminal pinnae replaced (or aborted) by bulbils...................................................................................... Danaea jenmanii Underw.

4. Terminal pinnae present, never replaced or aborted by bulbils.........................................................................................................5.

5. Pinnae narrow 1.0– 1.5 cm wide, 5–9 cm long ............................................................................................... Danaea urbanii Maxon

5. Pinnae wider, 1.1–2.4 cm wide, 6.8–15.0 cm long.................................................................................... Danaea mazeana Underw.

6 (1). Rhizomes creeping, sometimes with the tip ascending, dorsiventrally arranged, with all roots on the lower side and leaves in two or more rows; leaves usually iridescent................................................................................................ Danaea iridescens Christenh.

6 (1). Rhizomes erect, with roots and leaves radially arranged; leaves not iridescent ...............................................................................7.

7. Terminal pinnae much larger than largest lateral pinnae of the same leaf ............................................................ Danaea ulei Christ

7. Terminal pinnae of the same size or smaller than the largest lateral pinnae of the same leaf...........................................................8.

8. Rhizomes tall and slender, up to 110 cm long; leaves well-spaced. Lateral pinnae dull above, abruptly acuminate .......................... .......................................................................................................................................... Danaea arbuscula Christenh. & Tuomisto

8. Rhizomes shorter and stout, up to 50 cm long; leaves more crowded; lateral pinnae usually glossy above, gradually acute to longacuminate..................................................................................................................................................... Danaea geniculata Raddi