Bouteloua curtipendula var. caespitosa Gould & Kapadia

Authority

Kapadia, Z. & Gould, Frank W. 1964. Biosystematic studies in the Bouteloua curtipendula complex. IV. Dynamics of variation in B. curtipendula var. caespitosa. Bull. Torrey Bot. Club. 91: 465-478.

Family

Poaceae

Scientific Name

Bouteloua curtipendula var. caespitosa Gould & Kapadia

Type

TYPE: ARIZONA: 3 mi e of Bisbee on road right of way along cut, ea 5200 ft elev., 10 Aug 1962, Gould 10021. Holotype, TAES; isotypes, ARIZ, DS, GH, NY, TEX, UC, US. Fig. 43.

Description

Latin Diagnosis - Culmi rigidi erecti plerumque crassi caespitosi; stolones et rhizomata desunt. Folia plana vel subinvoluta, plerumque rigida crassaque sed variabillima. Inflorescentia variabilis ramis paucis vel numerosis cum spiculis paucis (raro 1) vel ad 9 in quoque ramo. Chromosomata aneuploidea somatica ea 58 ad 103. Pollen grande sed varians plerumque diametro 37-40 micra.

Species Description - Culms stiffly erect, from ea 0.5-1.0 m tall, usually stout and in large clumps, often from a hard "knotty" base; stolons and creeping rhizomes not developed. Leaf blades variable in width but most frequently narrow, typically thick and stiff. Infloreseence highly variable, with few to numerous branches, with an aver- age of 2-7 spikelets per branch. Spikelet color from bronze, yellowish-brown or straw-colored to green or various shades of purple. Anthers usually yellow or orange, infrequently red or purple. Chromosome nuLmber aneuploid, varying from 2n = 58 to 103.

Discussion

Bouteloua racemosa Lag., Var. Ci. 4: 141. 1805.

Atheropogon acuminatus Fourn., Mex. P1. Gram. 2: 139. 1881.

Bouteloua curtipendula var. caesp,itosa as presently interpreted is comprised of caespitose plants with high, mostly aneuploid chromosome numbers. Morpho- logical and cytological differences in these plants indicate that they have evolved through hybridization of various combinations of diploid and tetraploid taxa of the B. curtipendula complex. Reproduction is by seed, but seed set probably is by both sexual and apomictic processes.

Chromosome counts or approximations of chromosome numbers were made from PMC divisions for a large number of plants. Characteristically the segre- gation of chromosomes at PMC Division I was unequal, most frequently with 8-15 chromosomes moving to one pole and 80-90 chromosomes to the other (Gould 1959). The larger mass of chromosomes actually underwent little or no move- ment and remained loosely aggregated in the equatorial region throughout Division I. In Division II of both the laroe and the small cells, the chromosomes lined up regularly on the equatorial plate at metaphase and there was little or no lagging of chromosomes durinig aniaphase. Tetrads of two large and two small thick-walled, starch-filled pollen grains characteristically were formed. As would be expected, in many plants there was a high percent of unfilled pollen grains, in some more of the small type, in others more of the large type.

The few plants with chromosome numbers of less than 2n = 70 referred to B. cutrtipendula var. caespitosa tended to have equal or nearly equal segregation of chromosomes during PMC divisions. Though not cytologically typical of the variety, these plants were caespitose and morphologically inseparable from those with higher chromosome numbers and unequal segregation of chromosomes during PMC divisions. Gould 8966b from Parral, Mexico, was a caespitose plant with 2n = 58 chromosomes. Sampled at the same locality was a caespitose plant (Gould 8966g) with very different aspect and a chromosome number of 2n 84. Still another caespitose plant from the site (Gould 8966d) had 2n = 40 or 41 chromosomes. This plant, with slender wiry culms, tentatively has been referred to B. curtipendula var. tenuis.

A major "variant" from the widespread B. curtipendula var. caespitosa type occurs in north-central Mexico, from Tamaulipas, Nuevo León, and southern Coahuila southward to Mexico and Durango. These plants have "knotty", firm, much-branched and somewhat sod-forming culm bases. The culms are slender and short to moderately tall. Typically the inflorescence is short and with relatively few branches, these usually bearing only 1-3 spikelets. The spikelets characteristically are larger and deep purple in color.

The few plants of this type examined cytologically had chromosome numbers from 2n = 69 to 82 and little or no segregation of chromosomes during PMC Division I. Pollen tetrads of 2 large and 2 small spores were formed, but the latter, usually containing no chromosomes, soon shrivelled.

Three collections have been made of a striking "variant" of B. curtipendula var. caespitosa with stiffly erect rather than pendulant, infloreseence branches. At first glance, infloreseences of this type appear superficially similar to those of species of Agropyron. Garden seedings, however, have shown the erect inflorescence branch character to be highly unstable and not consistent even in seedlings grown from parent plants with erect branches.

Distribution

In North America, from southwestern U. S. through northern and central Mexico south to Oaxaca. In South America, reported from Venezuela, Bolivia, Uruguay, Argentina and Peru.

United States of America North America| Mexico North America| Venezuela South America| Bolivia South America| Uruguay South America| Argentina South America| Peru South America|