Blechnum gracile Kaulf.

Authority

Mickel, John T. & Beitel, Joseph M. 1988. Pteridophyte Flora of Oaxaca, Mexico. Mem. New York Bot. Gard. 46: 1-580.

Family

Blechnaceae

Scientific Name

Blechnum gracile Kaulf.

Description

Species Description - Rhizome erect, short-creeping to ascending, stoloniferous; rhizome scales concolorous, brown to dark brown, narrowly lanceolate, 1-3 mm long, 0.5-0.8 mm wide, margin with rare teeth; fronds clumped; stipe 1.8-22 cm long, 1/8-½ the frond length, stramineous, papillate, with sparse scales (similar to those of rhizome) at base, undercoat of matted, appressed hairs; sterile blade 8-20 cm long, 3-11 cm wide, pinnate; pinnae l-3(-4) pairs, distant, basal pinnae slightly reduced, apex conform, 1.5-2 times size of lateral pinnae, base of terminal pinna with 0-2 semicircular confluent to distinct lobes (4-5 mm diam.); rachis stramineous, glabrous, papillate, grooved; largest lateral pinnae 2.5-6 cm long, 6-14 mm wide, bases subcordate to cuneate, terminal pinna 614 cm long, 10-20 mm wide, lower surface glabrous or with rare, 2 mm long catenate hairs, upper surface glabrous, midvein grooved; veins forked, enlarged vein endings visible on upper surface; pinna margin serrulate, sometimes incurved; indusia ca. 2/3 of pinna, 1.5-4.5 cm long on lateral pinnae, 5-9 cm on terminal pinnae, 0.5 mm wide, subentire.

Discussion

Type. Brazil. Otto (B). Blechnum intermedium Link, Hort. berol. 2: 75. 1833. Type. Hort. Lips. (B; isotype NY!). Blechnum subdimorphum Copeland, Univ. Calif. Publ. Bot. 19: 288, t. 38. 1941. Type. Mexico. Veracruz: Cordova, Copeland 50 (MICH; isotypes P, UC). Blechnum fraxineum fide auct., non Willdenow, Sp. pi. 5: 413. 1810. Among the monomorphic taxa, Blechnum gracile is characterized by 1-3(-4) lateral pinna pairs, a conform caudate apex 1.5-2 times as long as the lateral pinnae with a subcordate base, usually 1-2 semicircular lobes below the apical pinnae, sometimes joined to the base, glabrous rachis and distant, glabrous pinnae with cuneate or subcordate bases. Part of the Blechnum occidentale complex (which see for fuller discussion of hybridization), this taxon, found from Mexico to South America and on Trinidad and Cuba, matches morphologically the tetraploid “B. fraxineum” of Walker (1966, 1973, 1985), analyzed from Trinidad. After careful karyotyping of both tetraploid and diploid “fraxineumhe considered that the tetraploid is a fertile allopolyploid of the diploid “fraxineum” and another fertile diploid, unknown at this time. The diploid “B. fraxineum” differs from the tetraploid “B. fraxineum” (=B. gracile) in having fertile and sterile leaves similar in size and shape (vs. narrower, somewhat dimorphic fertile fronds in the tetraploid), terminal pinnae similar in size and shape with the lateral pinnae (vs. much smaller and often rounded lateral pinnae in the tetraploid), and base of the erminal pinna is cuneate (vs. subcordate, with rounded lobes below in the tetraploid). This diploid taxon, which is found in South America, Trinidad, and Hispaniola, matches the type of B. longifolium Willdenow (Sp. pl. 5: 413, 1810. Type. Venezuela. Caripe, Humboldt 464, B-Willd. 20045!, tracing NY!; isotype P-Humb.!), which is a later homonym of B. longifolium Ca-vanilles, 1802 (=B. orientale), as well as the type of B. meridense Klotzsch (Linnaea 20: 349. 1847. Type. Colombia [Venezuela]. Mérida, Moritz 242 B!, tracing NY!; isotypes BM, NY!) and B. schlimense Fée (Mém. foug. 8: 71. 1857. Type. Colombia. Schlim 752 (P, fragment NY!; isotypes L (photo NY!), K (frag. NY!)). The type of B. fraxineum Willdenow (Sp. pl. 5: 413. 1810. Type. Venezuela. Caripe, Bredemeyer B-Willd. 20044!, tracing NY!) corresponds in morphology to the triploid hybrid of B. longifolium x occidental reported by Walker [as fraxineum x occidentale (2 x)] and discussed later, so the name B. fraxineum has been misapplied to the fertile taxa B. gracile (4 x) and B. meridense (2 x). Two specimens from Panama (Maxon 5162, Pittier 5307 (NY)) labelled as “Blechnum fraxineum Willd. var. ?” may possibly represent the other diploid parent of B. gracile. They have small fronds (6-8 cm long) and narrow terminal conform pinnae (4-5.5 cm long, 4-7 mm wide) that are 5-10 times longer than the single pair of lateral pinnae (0.6-1.1 cm long). These specimens appear to be the taxon recently named by L. D. Gómez (Phytologia 51: 474. 1982) as Blechnum lellingerianum [Type. Costa Rica. Puntarenas: Camarón to Cotón, 1300 m, Gómez 18139 (CR; isotype US!)]. Diploid Blechnum meridense (although apparently absent itself in Jamaica) forms sterile triploid hybrids with B. occidentale s.l. in Jamaica, Belize and Trinidad (Walker, 1966, 1973, 1985), which can form large populations through vegetative reproduction by stolons. These hybrids with B. occidentale are easily distinguishable by having too many pinna pairs for B. fraxineum (over four pinna pairs), having a caudate, semiconform apex about the same size as the lateral pinnae (not strictly pinnatifid like B. occidentale, but having gradually shorter pinnules at the base of the extended apex segment) and having truly pinnate blade base and widely distant median pinnae (thus eliminating B. polypodioides as a possible parent). These hybrids in Jamaica and Trinidad involve B. meridense (“fraxineum (2x)”) rather than B. gracile (“fraxineum (4 x)”) and have fertile fronds that are not narrowed significantly. The glabrous hybrid B. meridense x occidentale (matching the type of B. fraxineum) occurs in South America and Costa Rica, whereas the pubescent hybrid B. meridense x glandulosum (=B. x antillianum Proctor, 1965) occurs in Jamaica and South America. The hybrids of Blechnum gracile and B. occidentale or B. glandulosum have fertile fronds much narrower than the sterile, and are found in Mexico, Central Mexico, and South America. The hybrid B. glandulosum x gracile is uncommon in Chiapas (Breedlove 22456, NY), Guatemala (Bernoulli 456, NY), and South America. A specimen from Oaxaca (Hallberg 1292 (NY), Ixtlán, 400 m) corresponds to this combination, with narrower fertile fronds, semiconform tip, 8-10 pinna pairs and abortive spores. It occurs at a much lower elevation than does B. glandulosum. The corresponding hybrid between the glabrous Blechnum occidentale (in the narrow sense) and B. gracile, similar in morphology to the preceding hybrid but with glabrous rachises, is much more common in Central and South America. This hybrid has been collected in Costa Rica (several collections), Honduras (Nelson et al. 0217, Edwards P-688, Wilson 294 (NY)), Belize (Campbell 20, Gentle 3932, Jenman s.n. (NY)), Guatemala (Jones et al. 3077 (NY)), and South America. It occurs in Oaxaca at low elevations along both the Atlantic and Pacific slopes with one or the other of its parents. This sterile hybrid occurs in mixed collections with B. gracile from Tuxtepec (7381b, 300 m) and Juquila (6086b, 500 m), with B. occidentale s.s. from Choapan (Mexia 9181b (NY), 495 m) and Juchitán (6867b, 150 m), and alone in Pochutla (Morton & Makrinius 2716 (US), 800-1000 m) and Juchitán (Hernández G. 1523 (NY), 250 m).

Distribution

Terrestrial on banks and along streams in wet forest of low to middle elevation; Juquila, Pochutla, Putla, Tuxtepec; 20-800 m. Mexico (Gro, Ver, Oax, Chis); Guat to Pan; Cuba, Trin; Sur & Ven to Arg & Braz.

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