ANALYSIS OF A HYBRID COMPLEX BETWEEN BAPTISIA LEUCANTHA AND BAPTISIA VIRIDIS IN TEXAS

Abstract

IN THE preparation of a recent monograph of Baptisia it was found that frequent hybridism within the group furnished one of the principal bases for taxonomic confusion. Eight clear-cut cases-i.e., instances where both parents and the hybrid were found growing in close proximity were brought to light; and several suspected cases where marked intermediacy between the two supposed parents was exhibited, but which lack adequate evidence, were noted. MATERIALS AND METHODS.-One of the most suitable locations for study was discovered by Dr. Edgar Anderson and Mr. Leslie Hubricht in April, 1936, a few miles west of Beaumont, Texas, along a railroad track nearly to Pine Island. In a prairie habitat abounding in Gaura, pink evening primrose, etc., B. leucantha T. & Gr. and B. viridis Larisey were conspicuously hybridizing along a stretch several miles in extent. B. leucantha is a tall, erect, simply branched species with long racemes bearing numerous white flowers, the standards of which are striated toward the base. This was just coming into flower. B. viridis is a low, bushy, much-branched species with short racemes and yellow flowers having an unmarked standard. The latter was in full flower or passing. There was an abundance of yellow-flowered plants, a little white here and there, occasional Fls, and where the white-flowered type was the thickest there were a few apparent backcrosses to the yellow. A few clumps of B. leucophaea Nutt., a low spreading species with declined racemes and pale yellow flowers, were growing nearby, but apparently not entering in the complex. However, B. leuzcophaea var. glabrescens Larisey and B. viridis do hybridize in Louisiana (Harper, 1938) and elsewhere in southeastern Texas. Good herbarium specimens were made of each of the three entities, and in the area of greatest recombination herbarium specimens of one raceme and a few leaves from fifty-seven plants were selected at random as study material. Comparative studies of the two species and hybrid were made by assigning arbitrary index values to the most significant contrasting characters between B. leucantha and B. viridis, a plan suggested bv Dr. 1 Received for publication April 22, 1940. Edgar Anderson (1936). The index value of each individual equaled the sum of the values of its various characters. In this way it was possible to plot the entire lot on a chart which grouped the two species at the two opposite ends of the table, the hybrids in the middle, and probable backerosses scattered in the direction of the respective parent species (fig. 1). Pollen counts were also made, revealing a variable but higher percentage of bad pollen in the hybrids than in either of the two species (fig. 2). A list of the characters employed and the values assigned them follows in table 1; table 2 lists the index value and percentage of pollen fertility of all individuals involved. The plants in each of the three maj or categories were assigned arbitrary numbers to facilitate necessary reference to them. In accordance with current taxonomic practice a name, X B. fragilis, was assigned to the hybrid (Larisey, 1940). DIscussIoN.-Every character in either of the two parent species which might lend itself to biometric methods was checked for comparison and contrast, and in the end seventeen such characters were selected which furnished a very good index for the three major entities. 1. Glabrous vs. pubescent: B. leucantha is a glabrous species except for a sparse pubescence at the base of the leaflets and within the calyx lobes, characters common to virtually all species within the genus. B. viridis, on the other hand, is appressedpubescent throughout, especially on the leaf surfaces. In age there is a glabrate tendency, but rarely is there a loss of all pubescence. In the hybrids a sparse ciliation along the margins and midveins of the leaves and a slight appressed-pubescence along the stems and on the outer surface of the calyx lobes is apparent in varying degrees. 2. Black vs. green: As is the case in most species of Baptisia, B. leucantha blackens in drying, and sometimes in age while still in the living condition. B. viridis, on the other hand, belongs to a small group of species which nearly always retain their color. There is occasionally a darkening of the calyx lobes and of the mature pods, but in these instances the coloration is a deep bronze or brown rather than a jet black. The hybrids show an irregular discolora-