Monographs Details:
Authority:
Thomas, William W. 1984. The systematics of Rhynchospora section Dichromena. Mem. New York Bot. Gard. 37: 1-116.
Thomas, William W. 1984. The systematics of Rhynchospora section Dichromena. Mem. New York Bot. Gard. 37: 1-116.
Family:
Cyperaceae
Cyperaceae
Description:
Subspecies Description - Cespitose, mostly glabrous annual or short-lived perennial; culms arching to erect, 10-57 cm tall, 3-8 mm in diameter, green, triquetrous to obtusely so; leaves mostly cauline or from sterile shoots, flat, green, nerved, especially abaxially, often ciliate marginally at base of blade; basal leaves usually with reduced blades, sometimes only bladeless sheaths, occasionally with blades to 10 cm long and 3 mm wide; cauline leaves of fertile culm (2-)3-4(-5) with longest blades 7-21 cm long, 1.4-5 mm wide, flat to slightly involute, green, nerved; summit of inner band concave, hyaline only at summit or in a narrow, central strip; inflorescence bracts green, (3-)4-5 exceeding inflorescence, ciliate basally along margins, spreading to slightly reflexed (Figs. 3c, d); basal bract longest, 4-15 cm long, 1.5-4.5 mm wide; inflorescence a conical to hemispherical head of 3-6 spikelets; central spikelet largest, often much larger than others, ovoid, 7-12 mm long, 2.3-4.3 mm wide, consisting of ca. 20-30 scales; scales ferrugineous, ovate, 4.3-5.2 mm long, 1.8-3.6 mm wide, cymbiform, weakly carinate distally; filaments 4.3-5.8 mm long; anthers 1.8-1.9 mm long; stigma and style 3.8-4.9 mm long; stigma branches 1.1-3.3 mm long; achene (Figs. 10a, b) lenticular, bilaterally symmetrical, stramineous to orange-brown or bony-white, very widely obovate, 0.95-1.2 mm long, 0.8-1.35 mm wide; summit of achene arched or ± obtusely angled; shoulders of achene at edge of style base not confluent with margin of achene, or at least forming an angle; style base very shallowly triangular to shallowly lunate, 0.150.35 mm high, (0.6-)0.8-1.2 mm broad, brownish to stramineous or greenish; achene surface transversely rugulose; epidermal cells of achene narrowly elliptic, ± indistinct. Flowering and Fruiting: all year. Distinguishing Features: This subspecies differs from the typical subspecies by its large central spikelets surrounded by several smaller spikelets, its erect culm, the larger, spreading bracts and the smaller style base (Fig. 25). Like ssp. radicans, it is often viviparous (Fig. 3d). Robust specimens of ssp. microcephala approach R. watsonii but can be distinguished from that species by their fewer, shorter spikelets, narrower cauline leaves and lower number of bracts which exceed the inflorescence.
Subspecies Description - Cespitose, mostly glabrous annual or short-lived perennial; culms arching to erect, 10-57 cm tall, 3-8 mm in diameter, green, triquetrous to obtusely so; leaves mostly cauline or from sterile shoots, flat, green, nerved, especially abaxially, often ciliate marginally at base of blade; basal leaves usually with reduced blades, sometimes only bladeless sheaths, occasionally with blades to 10 cm long and 3 mm wide; cauline leaves of fertile culm (2-)3-4(-5) with longest blades 7-21 cm long, 1.4-5 mm wide, flat to slightly involute, green, nerved; summit of inner band concave, hyaline only at summit or in a narrow, central strip; inflorescence bracts green, (3-)4-5 exceeding inflorescence, ciliate basally along margins, spreading to slightly reflexed (Figs. 3c, d); basal bract longest, 4-15 cm long, 1.5-4.5 mm wide; inflorescence a conical to hemispherical head of 3-6 spikelets; central spikelet largest, often much larger than others, ovoid, 7-12 mm long, 2.3-4.3 mm wide, consisting of ca. 20-30 scales; scales ferrugineous, ovate, 4.3-5.2 mm long, 1.8-3.6 mm wide, cymbiform, weakly carinate distally; filaments 4.3-5.8 mm long; anthers 1.8-1.9 mm long; stigma and style 3.8-4.9 mm long; stigma branches 1.1-3.3 mm long; achene (Figs. 10a, b) lenticular, bilaterally symmetrical, stramineous to orange-brown or bony-white, very widely obovate, 0.95-1.2 mm long, 0.8-1.35 mm wide; summit of achene arched or ± obtusely angled; shoulders of achene at edge of style base not confluent with margin of achene, or at least forming an angle; style base very shallowly triangular to shallowly lunate, 0.150.35 mm high, (0.6-)0.8-1.2 mm broad, brownish to stramineous or greenish; achene surface transversely rugulose; epidermal cells of achene narrowly elliptic, ± indistinct. Flowering and Fruiting: all year. Distinguishing Features: This subspecies differs from the typical subspecies by its large central spikelets surrounded by several smaller spikelets, its erect culm, the larger, spreading bracts and the smaller style base (Fig. 25). Like ssp. radicans, it is often viviparous (Fig. 3d). Robust specimens of ssp. microcephala approach R. watsonii but can be distinguished from that species by their fewer, shorter spikelets, narrower cauline leaves and lower number of bracts which exceed the inflorescence.
Discussion:
Type: “Amer. merid.,” [Jamaica], Bertero s.n. (TO, holotype, not seen; MO, isotype; MICH, photograph of holotype). Rhynchospora microcephala (Bertero ex Sprengel) Kükenthal, Bot. Jahrb. Syst. 75: 311. 1951, non Rhynchospora microcephala Britton ex Small, Flora Southeastern U.S. 195, 1327. 1903. Rhynchospora pubera var. microcarpa Böckeler, Linnaea 37: 529. 1872. Type: Trinidad, Sieber 3 (MO, lectotype; M, isolectotype). Rhynchospora pubera forma elatior Duss, Annal. Inst. Colon. Marseille 3: 552. 1896. Syntypes: Martinique, Duss 706; Guadeloupe, Duss 3122, 3611 (F, NY). Pollination: I have not had an opportunity to watch for insect visitors to this species under ideal weather conditions. Nevertheless, in Jamaica, I observed several visits by unidentified insects and caught one specimen of Mesograpta cf. marginata (Diptera, Syrphidae). Although the spikelets are brown when mature, when in flower they are white and, to human eyes, are about as conspicuous as those of R. pubera which is often visited by insects. Nomenclature: The earliest description, previously overlooked, of either subspecies of R. radicans was Dichromena microcephala Bertero ex Sprengel, published in 1825. This precedes Schlechtendahl & Chamisso’s publication of Dichromena radicans by six years. The existence of R. microcephala Britton ex Small however, made KiikenthaFs combination under Rhynchospora of Bertero's epithet illegitimate.There is a discrepancy in the type locality as stated on the specimen (Jamaica) and in the description (“Amer. merid.”). “America meridionale” was normally used to refer to the South American continent while Caribbean islands were usually referred to by name or as the West Indies. There is little doubt that the Jamaican specimen is the type, because the only place in South America where Bertero collected extensively was in Chile, where species of section Dichromena are rare if they are present at all. There must either have been an error in the citation of the locality or the term “America meridionale” was used loosely. Discussion: There is an overlap or juxtaposition in the ranges of variation of most of the taxonomically important characters that separate ssp. radicans from ssp. microcephala. The ranges of variation of most of the quantifiable characters, such as spikelet number and style base size (Fig. 25), overlap very little but are juxtaposed closely enough to make identification difficult in many cases. Although they are fairly distinct entities in Mexico and the Antilles, they both occur in Central America and northern South America. Both geographically and morphologically these two taxa seem to form two ends of one cline. It is for this reason that I choose to recognize them as two subspecies of R. radicans.
Type: “Amer. merid.,” [Jamaica], Bertero s.n. (TO, holotype, not seen; MO, isotype; MICH, photograph of holotype). Rhynchospora microcephala (Bertero ex Sprengel) Kükenthal, Bot. Jahrb. Syst. 75: 311. 1951, non Rhynchospora microcephala Britton ex Small, Flora Southeastern U.S. 195, 1327. 1903. Rhynchospora pubera var. microcarpa Böckeler, Linnaea 37: 529. 1872. Type: Trinidad, Sieber 3 (MO, lectotype; M, isolectotype). Rhynchospora pubera forma elatior Duss, Annal. Inst. Colon. Marseille 3: 552. 1896. Syntypes: Martinique, Duss 706; Guadeloupe, Duss 3122, 3611 (F, NY). Pollination: I have not had an opportunity to watch for insect visitors to this species under ideal weather conditions. Nevertheless, in Jamaica, I observed several visits by unidentified insects and caught one specimen of Mesograpta cf. marginata (Diptera, Syrphidae). Although the spikelets are brown when mature, when in flower they are white and, to human eyes, are about as conspicuous as those of R. pubera which is often visited by insects. Nomenclature: The earliest description, previously overlooked, of either subspecies of R. radicans was Dichromena microcephala Bertero ex Sprengel, published in 1825. This precedes Schlechtendahl & Chamisso’s publication of Dichromena radicans by six years. The existence of R. microcephala Britton ex Small however, made KiikenthaFs combination under Rhynchospora of Bertero's epithet illegitimate.There is a discrepancy in the type locality as stated on the specimen (Jamaica) and in the description (“Amer. merid.”). “America meridionale” was normally used to refer to the South American continent while Caribbean islands were usually referred to by name or as the West Indies. There is little doubt that the Jamaican specimen is the type, because the only place in South America where Bertero collected extensively was in Chile, where species of section Dichromena are rare if they are present at all. There must either have been an error in the citation of the locality or the term “America meridionale” was used loosely. Discussion: There is an overlap or juxtaposition in the ranges of variation of most of the taxonomically important characters that separate ssp. radicans from ssp. microcephala. The ranges of variation of most of the quantifiable characters, such as spikelet number and style base size (Fig. 25), overlap very little but are juxtaposed closely enough to make identification difficult in many cases. Although they are fairly distinct entities in Mexico and the Antilles, they both occur in Central America and northern South America. Both geographically and morphologically these two taxa seem to form two ends of one cline. It is for this reason that I choose to recognize them as two subspecies of R. radicans.
Distribution:
Brazil South America| South America| Central America| Ecuador South America| Peru South America| Bolivia South America| Colombia South America| Venezuela South America| Guyana South America| Suriname South America| French Guiana South America|
Brazil South America| South America| Central America| Ecuador South America| Peru South America| Bolivia South America| Colombia South America| Venezuela South America| Guyana South America| Suriname South America| French Guiana South America|