Plagiobothrys (popcorn flowers) is a genus of low annual
or perennial herbs comprising of about 60 species. The distribution
of Plagiobothrys is concentrated in Chile, southwestern
United States, and northwestern Mexico (Johnston 1927 ). Plagiobothrys
species tend to be found in moist areas, and several species occupy
sensitive vernal pool habitats (The Jepson Manual, Hickman ed.
1993).
The plants of Plagiobothrys are low annual or perennial
herbs The frequently basal leaves are opposite and often connate-perfoliate
with the exception of Plagiobothrys collinus which has
varied leaf arrangement. The inflorescence is a naked or bracted
helicoid cyme. The calyx is often cut almost to base into lanceolate
or oblong erect or connivent lobes. In some taxa, the sepal bases
in the mature calyx are fused into a cup containing the fruits,
and is sometimes circumscissile. Short-pedicellate or subsessile
flowers are white with a short corolla tube that barely surpasses
the calyx. Petal lobes are rounded, spreading and imbricate. The
throat can be white or yellow, with intruded appendages. The gynobasic
style is slender, and usually short. The stigma is capitate or
turbinate. The gynobase is low-convex, pyramidal or "frustate"
(Johnston, 1923). Each of the two locules in the ovary are divided
early in development by false septa. At maturity the ovary develops
into four or sometimes two nutlets each of which contains a seed.
The nutlets are erect, ovate to lanceolate, smooth or roughened.
The position of the nutlet attachment scar (from attachment to
the gynobase) is described by Johnston (1923) as basal to medial.
The scar can be on, below or at the base of a strong ventral keel
(ventral ridge), or rarely the stipitate terminal elongation of
the ventral keel.
Morphology of the unit fruits, nutlets, is of extreme importance
in delimiting species within the Tribe Eritrichieae. Nutlet morphology
may also provide potential apomorphies that identify monophyletic
groups within Eritrichieae and Plagiobothrys. Preliminary SEM
images of nutlet pericarps from Plagiobothrys and exemplars
of other genera within Eritrichieae reveal previously unsuspected
characters. Once coded, these characters will be added to a data
matrix and will be used to resolve phylogenetic and taxonomic
questions.
Plagiobothrys belongs to the family Boraginaceae, subfamily
Boraginoideae, and Tribe Eritrichieae. Plagiobothrys has
formerly been classified as six former genera: Allocarya, Plagiobothrys,
Sonnea, Echidiocarya, Glyptocaryopsis, and Echinoglochin
(Johnston 1923, Munz 1973). The genus in not united by a known
apomorphy. It is my hypothesis that Plagiobothrys is a
paraphyletic group that needs revision. My most recent analysis
of Parsimony (PAUP), run with a data collected so far, supports
this hypothesis. I am still in the process of collecting data
for analysis, the monophyly of the genus will be retested when
I have a compete data set.
The goals for this thesis are: 1) to evaluate the monophyly of the genus Plagiobothrys; identify monophyletic subgroups within Plagiobothrys and evaluate the monophyly of the existing sections in the genus Plagiobothrys; and 2) to evaluate the validity of a putative new species within the genus Plagiobothrys using the phylogenetic species concept. My objectives are to: qualitatively describe nutlet pericarp ultrastructure characters from SEM images taken from 10 individuals from 11 glochidiate species, from SEM images taken from single individuals from the remaining 49 Plagiobothrys species, and from SEM images taken from single exemplars from 29 genera in the tribe Eritrichieae; and quantify four fruit morphological characters from 25 individuals from each of eleven glochidiate species in the genus Plagiobothrys. Quantified variation within and between taxonomic units will be statistically analyzed and graphed. Both qualitative and quantitative characters will be coded and entered into a data matrix using the software MacClade. The software PAUP will be used for analysis of parsimony. Character evolution will be traced on strict, semistrict, and Adam's consensus trees. Taxonomy of this genus, which has been treated as four genera in the past, will be evaluated and revised based on the phylogenetic relationships hypothesized by this research.
Publications in progress:
Dellavalle, M. & M. G. Simpson. Phylogenetic analysis of the genus Plagiobothrys (Boraginaceae), with emphasis on fruit wall ultrastructure.
Dellavalle, M. & M. G. Simpson. Fruit ultrastructure of Plagiobothrys (Boraginaceae), proposed for publication in Proceedings of the San Diego Natural History Museum.