(Swartz) Hooker, Gen. Fil. plate 111A. 1842.
Ray spiked fern
Swartz, Syn. Fil., 150, 379. 1806;
Plants extremely variable in size, 5--50 cm, those in leaf mold (only form known in flora) usually small, those in open sunny areas much larger. Leaves 1--60; rays 1--12, 4--40 mm; petioles 0.5--2 cm. 2 n = 168 (Trinidad).
Small individuals of Actinostachys pennula have sometimes been called A . germanii , but plants conforming to A . germanii are merely at the end of a morphological series; they are probably juvenile. Each juvenile has a large bulbous gametophyte remaining attached (a so-called "tuber") that is sometimes mistaken for the stem. Not only is the persistent gametophyte mistaken for a stem, but in the large forms of typical A . pennula the stem is not a solitary structure. Instead it resembles a compact, intergrown bush, made up of numerous tiny, narrow stems, usually less than 1 mm diam., that proliferate from old leaf bases---a type of cauline organization apparently unknown in any other living fern but possibly found in the fossil genus Tempskya . Measurements for plants in the North American flora are all in the lower parts of the range for the species. Actinostachys pennula is among North America's most unusual ferns, a highly treasured species, sought by field botanists who must, however, respect its rarity.