SYSTEMATIC STUDIES IN THE PHACELIA HUMILES GROUP (HYDROPHYLLACEAE): COROLLA VENATION PATTERNS

A survey of corolla venation patterns in the Phacelia Humiles group (Hydrophyllaceae) revealed considerable diversity, ranging from open venation and no interpetal vascular connections in some taxa to closed venation and interpetal vascular connections in others. In general, the distribution of the different venation patterns agrees with recent taxonomic treatments and provides evidence for the artificiality of sections based on ovule number. In several cases where the affinity of a species was ambiguous, the venation pattern of its corollas provides evidence for its placement. THE THIRTY-THREE recognized species and four varieties of Phacelia currently placed in the Humiles group are annual taxa of subgenus Phacelia. One species, P. franklin/i, has been reported to be an annual or biennial (Gillett, 1960). The group is predominantly Califormian in distribution; only five of the 33 species are extra-Californian, and 23 are endemic to the state. Constance (1963, pers. comm.) established the Humiles group by placing together taxa that Howell had treated as related to P. humilis (1943), and to P. douglasii, P. linearis and P. pringlei (1945). Traditionally, the taxa of the Humiles group had been placed into two different sections on the basis of ovule number (Brand, 1913). The species Howell related to P. humilis (four ovules per ovary) were assigned by Brand to section Euphacelia, and species Howell related to P. douglashi, P. linearis, and P. pringlei (more than four ovules per ovary) were assigned to section Eutoca. While noting similarities between the species assigned to these different sections, Howell maintained the ovule-based separation of the taxa. Constance's treatment was an effort to restructure the genus along more natural lines based upon overall morphology and recently obtained cytological information. The formation of the Humiles group from taxa that Howell had treated as belonging to two different sections raises questions as to the i Received for publication 29 December 1983; revision accepted 26 August 1985. I wish to thank Donald Kyhos for his advice and support during this project, Lincoln Constance for many valuable insights into the systematics of Phacelia, and J. T. Howell for doing the taxonomic research which made this paper possible. This study was supported in part by grant DEB7908608 from the National Science Foundation, and by a Grant-in-Aid of research from Sigma Xi. Their support is gratefully acknowledged. affinities of the species within this group, a question not addressed by Constance. In this paper, corolla venation patterns are used to evaluate relationships within the Humiles group, and to reaffirm the artificial nature of sections based on ovule number. MATERIALS AND METHODS-The corollas used in this study were taken from the author's collections and borrowed herbarium material (Appendix 1). Over 450 corollas were examined from 34 different taxa. Of the species referred to the Humiles group, only P. hardhamiae Munz and P. novenmillensis Munz were not included in this study. Permanent slides of the corollas are deposited at DAV. The specimens were prepared by rehydrating dried corollas in 1% Aerosal OT and staining in 1% safranin in 95% ethanol for 24 hr or more. Excess stain was removed with water. The corollas were then immersed in 0. 5% picric acid in 95% ethanol for approximately 10 seconds, followed by a 45-second immersion in 95% ethanol with five drops of ammonium hydroxide per 100 cc. Finally, they were placed in 100% ethanol for 10 seconds before being mounted in Euparal. For most of the figures the venation of the central petal was drawn with a camera lucida. The other petals were hand drawn by the author. The individual petals of each figure were taken from several different plants and were selected to encompass the variation observed in each taxon. RESULTS-The corolla venation patterns (CVP) in the different species of the Humiles group share one feature in common: there is a main central vein and two main lateral veins. The lateral veins either connect to the central vein at or near its base, or they may enter the corolla separately from the central vein. The