Species delimitation and recognition in the Pediomelummegalanthum complex (Fabaceae) via multivariate morphometrics

Abstract

Pediomelum is a genus endemic to North America comprising about 26 species, including the megalanthum complex, which consists of Pediomelummegalanthum and its varieties retrorsum and megalanthum, Pediomelummephiticum, and the recently described Pediomelumverdiense and Pediomelumpauperitense. Historically, species of the megalanthum complex have been variably recognized at the species or variety levels, dependent upon the relative importance of morphological characters as diagnostic of species. Ten quantitative morphological characters regarded as diagnostic at the species level were analyzed using multivariate morphometrics across these taxa in order to examine the discriminatory power of these characters to delineate species and to aid in species delimitation. The analyses support the recognition of Pediomelummegalanthum, Pediomelummephiticum, and Pediomelumverdiense at the species level, Pediomelumretrorsum as a variety under Pediomelummegalanthum, and suggest the sinking of Pediomelumpauperitense into Pediomelumverdiense. The findings of the present study help quantify the power of certain characters at delimiting taxa and provide a basis for taxonomic revision of the Pediomelummegalanthum complex.

Keywords: Fabaceae; Pediomelum; cluster analysis; multivariate morphometrics; principal component analysis; species delimitation.

Figure 1.

Dendrogram based on all characters for all specimens using Ward’s cluster analysis.

Figure 2.

Dendrogram using Ward’s cluster analysis for Pediomelum mephiticum, Pediomelum verdiense, and Pediomelum pauperitense.

Figure 3.

Principal component analysis ordination diagram incorporating all specimens with symbols according to initial identifications. m Pediomelum mephiticum, v Pediomelum verdiense, p Pediomelum pauperitense, ● Pediomelum megalanthum var. megalanthum, + Pediomelum megalanthum var. retrorsum. Principal component scale on the left and bottom; unrotated factor loading scale on the top and right. Exact loading matrix vector lengths are listed in Table 5.

Figure 4.

Principal component analysis ordination diagram for A) PCA2 and B) PCA3. m Pediomelum mephiticum, v Pediomelum verdiense, p Pediomelum pauperitense, ● Pediomelum megalanthum var. megalanthum, + Pediomelum megalanthum var. retrorsum. Principal component scale on the left and bottom; unrotated factor loading scale on the top and right. Exact loading matrix vector lengths are listed in Table 5.

Figure 5.

Canonical plot of points and means from linear discriminant analysis of all species by all characters with groups defined as: m Pediomelum mephiticum, v Pediomelum verdiense, p Pediomelum pauperitense, ● Pediomelum megalanthum var. megalanthum, + Pediomelum megalanthum var. retrorsum. Inner circles by group are the 95% confidence region for containing the true overall mean of the group; the outer circles by group are the normal 50% contours, the normal ellipse region that contains 50% of the population for each group. Rays show the coordinate directions in canonical space.

Figure 6.

Scatterplot and linear regression of key distinguishing character traits for the MVP group. Fit of A) peduncle by calyx tube and B) bracts by flower sizes for Pediomelum mephiticum (m, blue color), Pediomelum verdiense (v, green color), and Pediomelum pauperitense (p, red color). All measurements in mm. Line is regression by taxon with accompanying 95% confidence band shaded.