BIOSYSTEMATICS OF THE BOTHRIOCHLOA BARBINODIS COMPLEX (GRAMINEAE)

The New World species of Bothriochloa 0. Kuntze are polyploids with 2n = 60, 120, 180 and 220 chromosomes and they reproduce sexually. Plants with 2n = 180 chromosomes constitute the extremely variable B. barbinodis (Lag.) Herter, which is subdivided into var. barbinodis, var. palmeri (Hack.) de Wet comb. nov., and var. schlumbergeri (Fourn.) de Wet comb. nov. The single collection with 2n = 220 chromosomes belongs with var. schlumbergeri. Plants resembling B. barbinodis in inflorescence structure but having well-developed pedicellate spikelets and 2n = 120 chromosomes are included in B. campii (Swallen) de Wet comb. nov. South American collections of B. springfieldii (Gould) Parodi differ from North American collections in having 2n = 60 rather than 120 chromosomes and in having larger inflorescences as does B. barbinodis. Variety australis de Wet. var. nov. is described to include them. BOTHRIOCHLOA BARBINODIS as recognized here includes a diverse group of plants with 2n = 180 chromosomes. It is widely distributed in the southern USA and extends across large areas of MViexico and Central and South America as roadside weeds. Some 400 collections of this and related species were studied in an effort to determine whether any discontinuities in morphological traits could be discovered that would allow for the recognition of species and varieties within the B. barbinodis complex. MATERIAL AND METHODS-Morphological data are based on field studies in the natural habitats of the collections and on herbarium specimens obtained from plants grown in a uniform nursery at the Oklahoma State University. Herbarium specimens of collections studied are filed with the Crop Evolution Laboratory at the University of Illinois. Chromosome numbers were determined from developing microsporocytes stained with aceto-carmine. MORPHOLOGY-The collection studied includes all the species recognized by Conzatti (1946), Solhns and Swallen (1955), Gould (1957), and Parodi (1958). The American species of Bothriochloamay be distinguished, the one from the other, by the following key characters: 1. Pedicellate spikelets about as broad and as long as the sessile ones, neuter or rarely male. 2. Inflorescence with 3-10 branches arranged along a 2-5-cm-long primary axis; branches usually not divided, rarely with the lower ones bearing 2-3 racemes. 3. Leaves narrowly linear-lanceolate, 2-5 'Received for publication 13 June 1968. Supported in part by grants GB-4644 and GB-7014 from the National Science Foundation. mm wide, glabrous to sparsely hairy near the base; sessile spikelets 4-6 mm long, often pitted; 2 = 120 B. wrightii. 3. Leaves broadly linear-lanceolate, 2-10 mm wide, glabrous to strongly pilose; sessile spikelets 5-7 mm long, often pitted; 2n = 60 B. hirtifolia. 2. Inflorescence with 5-20 branches arranged along a 4-10-cm-long primary axis; lower branches divided about 2-3 cm from the base; sessile spikelets 4-6 mm long, usually pittedleaves 3-10 mm wide, glabrous except near the base; 2n = 120 B. campii. 1. Pedicellate spikelets often involute, usuallv shorter than the sessile ones, neuter. 4. Inflorescence compact, with numerous divided, more or less erect branches arranged on a primary axis that exceed the lower branches in length; sessile spikelets 2-5 mm long, never pitted. 5. Inflorescence 20-25 cm long; sessile spikelets awned; culms robust; 2n = 120 B. alta. 5. Inflorescence 5-20 cm long; culms slender to robust. 6. Sessile spikelets awned; 2n = 60, 120 B. saccharoides. 6. Sessile spikelets awnless, or at most with a 2-5-mm-long mucro; 2n = 60 B. exaristata. 4. Inflorescence open or compact, with few to numerous spreading branches that are usually longer, or at least subequal to the primary axis; sessile spikelets 4-8 mm long, pitted or not pitted often in the same raceme. 7. Inflorescence usually with numerous, strongly divided branches, when few, racemes moderately hairy and up to 12 cm long; sessile spikelets 4-5 mm long; culms rather robust, with well-developed