8. Asplenium trichomanes L. ssp. trichomanes (maidenhair spleenwort) Pl. 2i,j; Map 8

Leaves 3–20 cm long, monomorphic. Petioles reddish brown to nearly black their entire length, shiny, the color extending to nearly the tip of the rachis. Leaf blades pinnately compound, linear in outline. Pinnae mostly opposite to subopposite on the rachis, 2.5–8.0 mm long, the median pinnae 4–7 mm long, oblong to ovate or wedge-shaped, the margins toothed or shallowly lobed, not auriculate, the base truncate to wedge-shaped, not overlapping the rachis. Veins not anastomosing. Spores 64 per sporangium. 2n=72. July–September.

Scattered through the Ozark and Ozark Border Divisions, locally north to Lincoln County ( U.S., Canada, Europe, Asia, Africa, Australia). Shaded crevices and ledges of sandstone, chert, or granite bluffs and boulders; rarely on cherty dolomite bluffs.

Subspecies trichomanes is a widespread, diploid cytotype that usually occurs on noncalcareous substrates. Its spores are 27–32 mm long. Plants of the tetraploid ssp. quadrivalens D.E. Mey. occur on calcareous substrates in North America and have spores that are 37–43 mm long (Moran, 1982). It has been collected in southwestern Illinois on bluffs immediately across the Mississippi River floodplain from Missouri. This cytotype should be searched for on shaded dolomite bluffs in the eastern Ozarks.

No sterile hybrids involving the maidenhair spleenwort have been recorded from Missouri to date. However, elsewhere this species has been documented to hybridize with A. pinnatifidum (A. ¥herb-wagneri W.C. Taylor & Mohlenbr.), A. platyneuron (A. ¥virginicum Maxon), A. rhizophyllum (A. ¥shawneense (R.C. Moran) H.E. Ballard), and A. ruta-muraria (A. ¥clermontae Syme).