Brachyotum microdon (Naudin) Triana

  • Authority

    Wurdack, John J. 1953. A revision of the genus Brachyotum (Tibouchineae-Melastomataceae). Mem. New York Bot. Gard. 8 (4): 343-407.

  • Family

    Melastomataceae

  • Scientific Name

    Brachyotum microdon (Naudin) Triana

  • Description

    Species Description - Trichomes minutely but densely roughened. Branchlets quadrangular, sparsely to densely strigulose to loose-strigulose. Petiole 4-20 mm. Blade 15-85 x 8-40 mm., elliptic or elliptic-lanceolate to ovate with the apex acute to rounded and the base obtuse to subtruncate, thinly coriaceous to chartaceous, the 3 primaries thinly impressed above and elevated below, an additional pair of marginals more or less distinctly developed, the numerous soon-reticulate secondaries obscure above and obscurely elevated below; above sparsely to moderately strigulose or strigose, the hairs 1-15/mm.2 with the basal 1/5-1/3 adherent and not abruptly expanded; below sparsely to moderately hirsute or strigulose (1-)2-15(-25)/mm.2, the glands solitary and sparse to very dense 5-80/mm.2 Flowers constantly 5-merous, mostly ternate, sometimes with a pair of additional flowers at the node below the dichasial node or with still another pair at the next-lower node, occasionally the dichasia ternate, the dichasia subtended by persistent slightly reduced leaves. Pedicel 2-60 mm. below the bracteoles, 3-15 mm. above; pedicellar bracteoles (or bracts) 5-25 x 1-8 mm., 3-nerved, linear or narrowly elliptic to spatulate or narrowly ovate, sometimes leaf like, caducous in late bud or persistent until fruit, pubescent as the leaves or the smaller glabrous above. Hypanthium 5-9 x 4-8 mm., fleshy and 0.5-1.4 mm. thick medianly, moderately to densely short- to long-strigulose, the hairs (10-)15-25(-40)/mm.2 Sepals (3-)4-6(-7) x (3-)4-5 mm., united at bases 1—2(—3) mm., the lobes acuminate-triangular to triangular, the sinuses broad and rounded. Petals deep purple, (14-)16-19(-23) x (11-)13-l6(-21) mm., asymmetrically obovate with the apices very broadly obtuse to almost truncate and with small midvein acumens, the cilia 0.1-0.4 mm. (the terminal few to 1 mm.) and tipped with inconspicuous early-caducous glandular tips. Filaments (4-)5-7 mm., as long as the anthers; connective at anther base 1-1.8 mm., free of the anther 0.3-0.7 mm., the ventral lobing 0-0.6 mm. Style 20-36 x (0.5-)0.8-1.3 mm., apically tapered usually noticeably, exserted 4-15 mm. Ovary 5.5-10.5 x 3.5-5 mm., moderately to densely strigulose to short-strigose on the apical 3-7 mm., the apical lobes 1-4.5 mm. above the locules.

    Distribution and Ecology - Distribution: northwestern Bolivia to extreme northwestern Argentina, alt. 1900-3800 m.

  • Discussion

    Chaetogastra microdon Naudin, Ann. Sci. Nat. III. 14: 132. 1850.

    Cbaetogastra pentlandii Naudin, Ann. Sci. Nat. III. 14: 133. 1850.

    Chaetogastra bermannioides Naudin, Ann. Sci. Nat. III. 14: 133. 1850.

    Brachyotum pentlandii (Naudin) Triana, Trans. Linn. Soc. 28: 49. 1871.

    Brachyotum hermannioides (Naudin) Triana, Trans. Linn. Soc. 28: 49. 1871.

    Brachyotum setosum Gleason, Mem. N. Y. Bot. Gard. 7: 314. 1927.

    Type Collection and Locality: D'Orbigny 481 (HOLOTYPE P); near "Carcuata- Yungas." This locality is perhaps Circuata, Dept. La Paz, Bolivia. Type Photographs and Illustrations: F36132 (HOLOTYPE); New York s.n. (holotype of Cbaetogastra hermannioides); F36128 (isotype of Chaetogastra hermannioides at P); F36138 (presumed holotype of Chaetogastra pentlandii at P); New York s.n. (holotype of Brachyotum setosum)', Ann. Sci. Nat. III. 14: pl. 4, f. 6 (1850) (as Cbaetogastra hermannioides).

    There are no noticeable criteria for specific delimitation of the three epithets here involved. The "pentlandii" element would typically be represented by specimens with compact inflorescences, elliptic round-tipped leaf blades (15-35 x 8-16 mm.)with length/width ratio of 1.8-2.6 and with the upper surfaces sparsely strigulose (1-2/mm.2), sparsely strigulose branchlets, and ovary apex lobes 2-4.5 mm. long: Pentland s.n., Nichols & Eggers s.n..White 151, Cardenas 3214, and Bridges s.n. Similar but with upper leaf surface pubescence 2-7/mm.2 and ovary apex lobes 1-1.5 mm. long are Balls B6249 p.p.. (US p.p.), Steinbach 8667, Herzog 1913, and Cuming s.n. With similar leaf shape but denser and longer upper leaf surface pubescence (6-14/mm.2) and very loosely appressed dense branchlet pubescence are Werdermann 2015, Steinbach 8512, and most of Balls B6249, although the lastnamed collection has great variation in pubescence density. Balls B6277 ranges from sprigs similar to Balls B6249 to some approaching the northern "hermannioides" element (but with contracted inflorescences); also similar to the northern "hermannioides" phase is Steinbach 5948. In part overlapping these last two collections to some extent is a "microdon" element with compact inflorescences, elliptic-lanceolate acute-tipped leaf blades with length/width ratio of 2-3.6 and with the upper surfaces moderately strigulose ((3-)5-8(-11)/mm.2), generally very loosely appressed branchlet pubescence, and ovary apex lobes 1.5-2.5 mm. long. This group includes all other specimens from Depts. La Paz and Cochabamba, except Cardenas 3056 which has a leaf blade length/width ratio of 2.6-3 but ovary apex lobes 3.7-3.9 mm. long. In all the foregoing groups, the pedicellar bracteoles are mostly caducous before anthesis and generally are linear to very narrowly spatulate (5-14 x 0.7-4 mm.); the pedicels are 2-7(-11) mm. long below the bracteoles. With leaf shape and size as in Balls B-6277 p.p. and Steinbach 5948 (ovate and acute-tipped, 20-40 x 10-20 mm.), but branchlet pubescence sparse and strictly appressed, the upper surfaces of the leaf blades sparsely shortstrigose (1-3/mm.2), the pedicels 10-20 mm. long below the bracteoles, and the persistent bracteoles 8-11 x 1.5-3.5 mm., is a northern "hermannioides" element: Weddell 3783, Weddell 3784, and Carriker s.n. The southern "hermannioides" element, consisting of Fiebrig 2458, Fries 1283, and all Argentinian specimens, is similar but shows larger leaves (30-85 x 20-40 mm.), variation in length of pedicels below bracteoles of 6-60 mm., and persistent bracteoles 10-41 x 2-11 mm. While the morphologic variation between the extremes is great, even varietal delimitation within B. microdon will be difficult and has been deferred.

    No immediate relatives of B. microdon are apparent. The pubescence is somewhat suggestive of B. ledifolium. Perhaps a closer relative is B. floribundum, which differs in type of pubescence, development of inflorescence, and size of flowers.