Monographs Details – Flora of Las Orquideas National Park

Monographs Details:

Authority:

Maas, Paulus J. M. 1972. Costoideae (Zingiberaceae). Fl. Neotrop. Monogr. 8: 1-140. (Published by NYBG Press)

Family:

Costaceae

Scientific Name:

Costus laevis Ruiz & Pav.

Synonyms:

Costus giganteus Kuntze, Costus kuntzei K.Schum., Costus pulcherrimus Kuntze, Costus splendens Donn.Sm., Costus maximus Schum., Costus cylindricus var. pulcherrima (Kuntze) Jacq. & Schum., Costus weberbaueri Loes., Costus skutchii C.V.Morton

Description:

Description - Plants stout 0.5-6 m tall, usually brown when dry. Sheaths glabrous or nearly so, 1-2(-4) cm in diam. Ligule obliquely truncate, 5-15 mm long, glabrous. Petiole 5-2o(-3o) mm long, glabrous or rarely sparsely sericeous. Leaves narrowly elliptic to narrowly obovate, long-acuminate at the apex (acumen to 30 mm long), cuneate at the base, occasionally rounded or cordate, 15-50 cm long, 4-16 cm wide, upper side glabrous or rarely puberulous, costa often strigulose, lower side glabrous or rarely densely puberulous. Inflorescence broadly cylindric to ovoid, 5-10 cm long, elongating to 25 cm in fruit, 3-7 cm wide, to 9 cm in fruit, terminal on a leafy stem or rarely on a separate flowering stem to 50 cm tall, sheaths obliquely truncate, 3-6 cm long, 7-10 mm wide, glabrous to rather densely strigulose. Bracts green to yellowish green, or occasionally red in the exposed part, red in the covered part, coriaceous, broadly ovate, obtuse, 2.5-5(-6.5) cm long, 3_4-5 cm wide, the covered part glabrous to rather densely puberulous, the exposed part glabrous, callus yellowish, to 15 mm long. Bracteole 20-30(-35) mm long, glabrous to rather densely puberulous. Calyx 6-15(-20) mm long, glabrous to rather densely puberulous, lobes deltate to shallowly triangular, 2-5 mm long. Corolla yellowish to reddish white, 50-75 mm long, glabrous, tube 15-25 mm long, lobes narrowly obovate, 35-50 mm long, 15-25 mm wide. Labellum broadly obovate when spread out, 50-70 mm long, 40-55 mm wide, lateral lobes purple-red with yellow venation, or sometimes white to yellow without any venation, middle lobe recurved tri- to quinque-lobulate, blotched with yellow in the centre. Stamen narrowly elliptic, 35-50 mm long, 10-13 mm wide, apex reddish, reflexed, anther 6-12 mm long. Pollen size 98-112 µ. Exine 2-3 µ thick. Number of pores 7-8. Porus diam 16-30 µ (Garcia-Barriga 10953 and Haught 1913, both from Colombia). Ovary 4-12 mm long, sericeous to glabrous. Capsule ellipsoid, 8-20 mm long, glabrous, or puberulous at the apex, seeds black.

Discussion:

It should not be too difficult to recognize this species in the field. It is well marked by its large, broadly cylindric, usually green inflorescence, and by its flowers with a usually strongly purple-red striped labellum. Herbarium material of C. laevis is often characterized by the light to dark brown colour of the vegetative parts; besides, the long petioles and the extremely long and long-acuminate leaves are distinctive.

Its closest relative is C. acre anus, but that species has a somewhat longer calyx, and most flower parts are covered with a velutinous indument. Another relative is C. pictus, differing from C. laevis in its much shorter flowers and its characteristic, very short, usually red-brown ligule.

The material studied is not quite homogeneous, as is usual in many of the widespread species; part of the Colombian and Ecuadorian material was slightly divergent in having a short calyx (6-7 mm long) and some plants also in bearing the inflorescence on a separate leafless shoot. These specimens possibly represent a distinct variety, subspecies, or even species, but I prefer to wait for better material (fresh flower material) before drawing any final conclusion.

Three Ecuadorian specimens deviated by being densely puberulous to velutinous on the lower side of the leaves. The flower material being very incomplete I could not determine their taxonomic status, ie, whether it is a variety of C. laevis or a distinct species. These specimens are the following: Asplund 7833, 20068 (S), both from Rio Verde Grande, prov. Tungurahua, alt 1500 m, and Penland & Summers 179 (BM, F, MO) between Rio Mapoto and Rio Margaritas, prov. Tungurahua, alt 1225 m.

The identification of the following specimens is uncertain; I have named them C.? laevis, but they also show some resemblance to C. spiralis: Bang 912 (BM, C, F, GH, K, L, LE, MO, NY, US), Kuntze sn (NY), and Rusby 1295 (NY, US), all from Bolivia.