Research Article |
Corresponding author: Ashley N. Egan ( egana@si.edu ) Academic editor: Clifford Morden
© 2015 Ashley N. Egan.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Egan AN (2015) Species delimitation and recognition in the Pediomelum megalanthum complex (Fabaceae) via multivariate morphometrics. PhytoKeys 44: 65-87. https://doi.org/10.3897/phytokeys.44.8750
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Pediomelum is a genus endemic to North America comprising about 26 species, including the megalanthum complex, which consists of P. megalanthum and its varieties retrorsum and megalanthum, P. mephiticum, and the recently described P. verdiense and P. pauperitense. 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 P. megalanthum, P. mephiticum, and P. verdiense at the species level, P. retrorsum as a variety under P. megalanthum, and suggest the sinking of P. pauperitense into P. verdiense. 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 P. megalanthum complex.
Pediomelum , principal component analysis, multivariate morphometrics, species delimitation, cluster analysis, Fabaceae
Pediomelum Rydb. (Psoraleeae; Leguminosae) includes about 26 species, all native to North America (
An example of these contrasting taxonomic views can be found within the subspecific classification of P. megalanthum (Wooton & Standl.) Rydb. Some botanists have recognized this as having three varieties (e.g.
Given the narrow distributions of these taxa and the disparate views on the usefulness of certain morphological characters for species delimitation in this group, many might see this as an example of the age old war between lumpers, those who tend to recognize fewer species, often allowing considerable breadth of morphological variation as inherent in species concepts, and splitters, those who split species based on more minute morphological differences, sometimes down to the population level. Hewitt C. Watson eloquently exemplified this war in a letter to Charles Darwin dated 13 August 1855 wherein he wrote “Taking J. D. Hooker & Jordan as representative men for the opposite factions in botany,—‘lumpers & splitters’, the former would reduce the species of vascular plants to three score thousand, or perhaps much fewer;—while Jordan would raise them to three hundred thousand.” (Darwin Correspondence Database, 25 Sept 2014).
Whilst preparing the treatment of Pediomelum for the Flora of North America, I was confronted with the question of where I lie on the spectrum of lumpers vs. splitters, for P. megalanthum and its varieties, and in particular, in regards to two recent species described by
The rapid radiation of the genus coupled with the variable recognition of specific or varietal ranking and the contrasting opinions of the relative discriminatory power and usefulness of several morphological characters invites an approach using multivariate morphometric analysis as a means of delimiting species or varieties among contested taxa. This is particularly so in the case of the newly described P. pauperitense and P. verdiense. This work will additionally examine the relative power of certain quantitative morphological characters historically used to delimit species in this group. Here, I aim to objectively delimit species within the P. megalanthum complex using a multivariate morphometric approach, incorporating the morphological diversity of P. megalanthum (vars. megalanthum and retrorsum), P. mephiticum, P. verdiense, and P. pauperitense. I have chosen to recognize P. epipsilum at the specific level (discussed below) and so it is not included in these analyses.
Plant material – Twenty-seven herbarium specimens from Utah and Arizona (deposited at ARIZ, ASC, BRY, and US) were chosen for study and tentatively identified as P. mephiticum, P. megalanthum var. megalanthum, P. m. var. retrorsum, P. pauperitense, and P. verdiense. A list of the specimens included in the morphometric analyses, with voucher information and origin, are given in Table
Specimens and their source herbaria used for morphometric analyses. Only first collectors listed. *specimens listed as paratypes by
P. megalanthum var. megalanthum: (BRY) - Belnap 244, Licher 1915, Welsh 22771, Welsh 27822, Welsh 22787 |
P. megalanthum var. retrorsum: (BRY) - Bundy 140, Atwood 4798, Hughes 3 |
P. mephiticum: (BRY) - Baird 3080, Welsh 23478, Atwood 5148, Egan 126, Neese 16864; (US) - Atwood 3903, Holmgren 3290, Jones 5095, Jones 5064b |
P. pauperitense: (BRY) - Higgins 23137*, Atwood 18013 |
P. verdiense: (ARIZ) - Wojciechowski 212*, Harbison 41.312*, Demaree 43938; (ASC) - Rink 1840*, Licher 2347; (BRY) - Licher 2009, Licher 2015, Licher 2007. |
Characters scored – Ten quantitative morphological characters (Table
Character acronym | Detailed description of the character |
---|---|
flower length | from the base of the calyx to the tip of the banner |
calyx length | from the base of the calyx to the tip of the lower calyx tooth |
calyx tube | from the base of the calyx to the beginning of the calyx teeth |
lower calyx tooth | from point of attachment on calyx to tip |
stipules | from point of attachment to tip |
petioles | from point of attachment to base of petiolule |
leaflets | from point of attachment to petiolule to tip of terminal leaflet |
bracts | from point of attachment to tip |
peduncle | from point of attachment on stem to base of first pedicel |
pedicel | from point of attachment to peduncle to base of calyx |
Multivariate morphometric analyses – A combination of multivariate analyses and hierarchical clustering were employed to investigate species limits in this group. All statistics were computed in the statistical package JMP v. 11.1.1 (SAS Institute Inc., Cary, NC). As an initial step, correlation coefficients were computed on the total dataset and on each species’ dataset to reveal any highly correlated character pairs that may distort downstream analyses. In addition, departure from a normal distribution for each character within each species was tested using the Shapiro-Wilk goodness of fit test (
Morphometric multivariate analyses were conducted on values of individual measurements without averaging across multiple observations per specimen. This was done because of the limited number of specimens available for P. pauperitense and P. verdiense. Use of all observations both within and across specimens will likely provide a better view of the intraspecific variation within a character. This is akin to
A hierarchical cluster analysis (HCA) was performed to investigate how specimens would group based on overall morphological similarity using Ward’s minimum variance method with the data standardized by standard deviation (
Principal component analysis (PCA;
Canonical discriminant analyses (CAN) were employed to investigate the spread of means across each species group and determine how well the characters (Y) predicted the separation of species based on means. This method measures the distance of each point from the centroid, or multivariate mean, of its group as defined previously by species or subspecies. The distance measure is based on the Mahalanobis distance, which incorporates the variances and covariances between variables. CAN is classically implemented using a linear method, which assumes that Y variables are normally distributed with the same variances and covariances, or a quadratic method in which covariances can be different across groups. Because not all of the character distributions were normal, I employed a regularized, compromise method, which is a mixture between the linear and quadratic methods (
Among the multivariate analyses employed here, several have been used by other researchers to determine those variables causally impacting the separation of species. As a variable reduction technique, PCA helps to discern which characters are responsible for grouping individuals. However, it does not assume an underlying causal model. For determining those characters responsible for delineating species, factor analysis may be a more appropriate method as this technique makes the explicit assumption of an underlying causal model (
Each analysis was conducted on a series of three data sets or levels: (1) the first dataset included all species, (2) the second dataset includes only data from P. mephiticum, P. verdiense, and P. pauperitense (the MVP group), (3) the third data set includes the P. megalanthum varieties, P. m. var. megalanthum and P. m. var. retrorsum. Datasets are thus notated by the type of analysis and the dataset used such as CAN1, HCA2, PCA3, and so on.
Following
The vast majority of character distributions fit a normal curve, with three rejecting the null hypothesis of a normal fit only marginally (0.04 < p < 0.05; P. m. var. retrorsum:lower calyx tooth, P. mephiticum:peduncle & petioles), three rejecting moderately (0.02 < p < 0.04; leaflets for P. verdiense & P. pauperitense), three rejecting strongly (0.001 < p < 0.01; P. pauperitense:calyx tube*, P. m. var. megalanthum:flowers & petioles*), and one rejecting very strongly (p=0.0003; P. mephiticum:pedicel*), those distribution with outliers detected are notated with an asterisk. Summary statistics for each character by species are given in Table
Summary statistics for each character by species. number of observations (n), minimum (min) and maximum (max) values, mean, standard deviation (st. dev.), and 5th and 95th percentiles.
Taxon | Parameter | flower | calyx | calyx tube | lower calyx tooth | stipules | petiole | leaflets | bracts | peduncle | pedicel |
---|---|---|---|---|---|---|---|---|---|---|---|
P. megalanthum | Min–max | 12–18 | 11.8–16.2 | 4.8–8.1 | 6.5–10.2 | 6.8–12.4 | 44–150 | 16–33 | 5.7–13 | 8.5–80 | 3–6.2 |
var. megalanthum | Mean/St.dev. | 16/1.716 | 13.81/1.213 | 6.28/0.802 | 8.08/1.103 | 9.57/1.538 | 72.05/23.125 | 25.53/5.265 | 9.34/1.930 | 34.15/21.185 | 4.07/0.896 |
n=20 | 5-95 Quantiles | 12.03–17.98 | 11.81–16.16 | 4.81–8.07 | 6.5–10.19 | 6.81–12.38 | 44.1–147.25 | 16.15–32.95 | 5.74–12.98 | 8.59–79.5 | 3–6.17 |
P. mephiticum | Min–max | 9.4–12.6 | 8.2–11.7 | 2.6–4.1 | 5.3–8.3 | 7.4–14 | 32–120 | 15–35 | 6.8–12.5 | 19.7–65 | 2.3–5.7 |
n=34 | Mean/St.dev. | 10.94/0.583 | 10.12/0.798 | 3.52/0.399 | 6.74/0.734 | 9.69/1.427 | 64.76/23.745 | 24.36/5.195 | 10.1/1.428 | 40.64/13.099 | 3.09/0.734 |
5-95 Quantiles | 9.93–12.15 | 8.43–11.48 | 2.75–4.1 | 5.45–8.15 | 7.85–12.58 | 32.75–113.25 | 16.5–34.25 | 7.78–12.43 | 20.68–64.25 | 2.3–4.8 | |
P. pauperitense | Min–max | 10.7–12.2 | 9.8–12.1 | 4.2–5.5 | 5.5–7.9 | 8.7–13 | 57–98 | 14–28 | 3.6–7.3 | 17–54 | 3–4.2 |
n=10 | Mean/St.dev. | 11.53/0.585 | 10.84/0.869 | 4.59/0.465 | 6.49/0.791 | 10.54/1.377 | 71.7/14.345 | 19.6/5.211 | 5.83/1.218 | 33.7/11.814 | 3.62/0.405 |
5-95 Quantiles | 10.7–12.2 | 9.8–12.1 | 4.2–5.5 | 5.5–7.9 | 8.7–13 | 57–98 | 14–28 | 3.6–7.3 | 17–54 | 3–4.2 | |
P. megalanthum | Min–max | 14.8–19.8 | 12.2–16.2 | 6.2–7.7 | 6.4–9.6 | 7.6–12.9 | 40–94 | 18–29 | 6.8–12.3 | 19–62 | 3–5.1 |
var. retrorsum | Mean/St.dev. | 17.78/1.402 | 14.45/1.19 | 6.94/0.533 | 7.69/1.154 | 10.2/1.818 | 65.42/15.785 | 22.23/3.265 | 9.53/1.745 | 38.4/15.995 | 3.82/0.667 |
n=12 | 5-95 Quantiles | 14.8–19.8 | 12.2–16.2 | 6.2–7.7 | 6.4–9.6 | 7.6–12.9 | 40–94 | 18–29 | 6.8–12.3 | 19–62 | 3–5.1 |
P. verdiense | Min–max | 10.3–15 | 8.5–13 | 3–4.9 | 4.5–9 | 6–11.7 | 22–95 | 14–30 | 5–10 | 11–35 | 2.3–6 |
n=34 | Mean/St.dev. | 12.2/0.983 | 10.82/1.216 | 4.09/0.412 | 6.88/1.239 | 8.9/1.37 | 52.63/15.876 | 20.75/4.465 | 7.13/1.092 | 22.53/7.184 | 3.93/0.912 |
5-95 Quantiles | 10.43–14.03 | 8.7–13 | 3.2–4.84 | 4.89–9 | 6.13–11.7 | 23.95–84.6 | 14.65–30 | 5.46–9.35 | 11.65–34.35 | 2.56–6 |
Ward’s cluster analysis of all specimens (HCA1) produced a dendrogram with two main groups: one comprised of entirely P. mephiticum, P. verdiense, and P. pauperitense with the exception of a single P. m. var. megalanthum data point, and the other group comprised of three subgroups, two comprising mixtures of the two P. megalanthum varieties and one comprised mainly of P. verdiense (Fig.
The ordination diagram from the principal component analysis based on all specimens (PCA1; Fig.
Principal component analysis ordination diagram incorporating all specimens with symbols according to initial identifications. m P. mephiticum, v P. verdiense, p P. pauperitense, ●P. megalanthum var. megalanthum, + P. 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
Independent principal component analyses were also conducted on the two main subgroups defined by PCA1. PCA2, comprising the MVP group, showed good separation along the first axis of P. mephiticum from P. verdiense and P. pauperitense, with floral vs. vegetative characters strongly affiliated with this break (Fig.
Principal component analysis ordination diagram for A) PCA2 and B) PCA3. m P. mephiticum, v P. verdiense, p P. pauperitense, ●P. megalanthum var. megalanthum, + P. 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
Eigenvector contributions (PC) of each character from the first two axes of the principal component analyses based on all morphological characters incorporating all species (PCA1), the P. mephiticum-P. verdiense-P. pauperitense (MVP) complex only (PCA2), and for the two varieties of P. megalanthum (PCA3). Characters are described in Table
PCA1 (Fig. |
PCA2 (Fig. |
PCA3 (Fig. |
||||
---|---|---|---|---|---|---|
Character | PC1 | PC2 | PC1 | PC2 | PC1 | PC2 |
flower | 0.502 | -0.098 | 0.432 | 0.218 | 0.424 | 0.186 |
calyx | 0.522 | -0.095 | 0.362 | 0.484 | 0.405 | 0.413 |
calyx tube | 0.472 | -0.101 | 0.350 | -0.262 | 0.473 | -0.072 |
lower calyx tooth | 0.390 | -0.094 | 0.189 | 0.608 | 0.082 | 0.600 |
stipules | 0.097 | 0.229 | -0.162 | -0.004 | 0.201 | 0.195 |
petioles | 0.092 | 0.391 | -0.292 | 0.024 | -0.137 | -0.198 |
leaflets | 0.103 | 0.330 | -0.282 | 0.277 | -0.360 | 0.145 |
bracts | 0.150 | 0.536 | -0.389 | 0.342 | 0.324 | -0.426 |
peduncle | 0.116 | 0.536 | -0.366 | 0.270 | 0.235 | -0.176 |
pedicel | 0.191 | -0.272 | 0.220 | 0.111 | -0.278 | 0.345 |
Canonical and classificatory discriminant analyses were also conducted to investigate the spread of means per species group. In accordance with HCA and PCA analyses, CAN1 shows P. mephiticum largely distinct from the others, with the two P. megalanthum taxa creating one group while P. verdiense and P. pauperitense another (Fig.
Canonical plot of points and means from linear discriminant analysis of all species by all characters with groups defined as: m P. mephiticum, v P. verdiense, p P. pauperitense, ●P. megalanthum var. megalanthum, + P. 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.
Factor analyses and PCA were taken together to help elucidate those characters most influential in separating predefined groups based on expert identification (Table
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 P. mephiticum (m, blue color), P. verdiense (v, green color), and P. pauperitense (p, red color). All measurements in mm. Line is regression by taxon with accompanying 95% confidence band shaded.
Relative distinguishing power of characters between species by factor or PCA analyses. Bold factors are those highly associated with the corresponding loading.
FAPC-rotated loadings | FAML-rotated loadings | PCA-loading matrix | |||||
---|---|---|---|---|---|---|---|
All specimens | FA1 (32.2%) | FA2 (19.3%) | FA1 (26.6%) | FA2 (12.8%) | FA3 (12.5%) | PC1 (33.5%) | PC2 (17.9%) |
mvp|gr | m|vp | mvp|gr | m|vp | m|vp | mvp|gr | m|vp | |
flower | 0.917418 | 0.146258 | 0.951893 | 0.091466 | 0.02346 | 0.91974 | -0.13088 |
calyx | 0.951527 | 0.160732 | 0.914948 | 0.135937 | 0.192597 | 0.9566 | -0.12712 |
calyx tube | 0.865426 | 0.125783 | 0.838602 | 0.109935 | 0.475039 | 0.86402 | -0.13511 |
lower tooth | 0.718706 | 0.090375 | 0.243157 | -0.207947 | 0.216766 | 0.71338 | -0.12566 |
stipules | 0.078849 | 0.345099 | 0.044324 | 0.807081 | 0.096593 | 0.17714 | 0.30648 |
petioles | 0.006661 | 0.549323 | 0.003746 | 0.629476 | 0.071232 | 0.16841 | 0.52291 |
leaflets | 0.04924 | 0.477942 | 0.087371 | 0.278027 | -0.074971 | 0.18804 | 0.44215 |
bracts | 0.051288 | 0.765723 | -0.028996 | 0.236017 | 0.206967 | 0.27489 | 0.71652 |
peduncle | -0.008032 | 0.748081 | 0.125539 | 0.146123 | -0.014782 | 0.21301 | 0.71716 |
pedicel | 0.440783 | -0.24418 | 0.357629 | 0.015441 | 0.933736 | 0.34914 | -0.36334 |
MVP only | FA1 (25.5%) | FA2 (23.7%) | FA1 (20.3%) | FA2 (19%) | FA3 (12.9%) | PC1 (29.1%) | PC2 (20%) |
m|vp | vp|v | m|vp | m~vp | p~v | m|vp | vp|v | |
flower | -0.374642 | 0.705445 | 0.991576 | 0.090467 | -0.092824 | 0.73706 | 0.30781 |
calyx | -0.044509 | 0.920401 | 0.783954 | -0.304062 | -0.105493 | 0.61815 | 0.68338 |
calyx tube | -0.697581 | 0.092945 | 0.574663 | 0.254593 | -0.285595 | 0.59828 | -0.37056 |
lower tooth | 0.29626 | 0.868977 | 0.206384 | 0.173869 | 0.009934 | 0.32207 | 0.85975 |
stipules | 0.209798 | -0.179713 | 0.176519 | 0.973894 | 0.144094 | -0.27618 | -0.00589 |
petioles | 0.407106 | -0.289188 | 0.046761 | -0.393911 | 0.898281 | -0.49816 | 0.03461 |
leaflets | 0.620859 | -0.002673 | -0.131126 | -0.151598 | 0.410291 | -0.48171 | 0.3917 |
bracts | 0.819303 | -0.046928 | -0.038605 | -0.658242 | 0.367456 | -0.66321 | 0.48334 |
peduncle | 0.724966 | -0.100322 | -0.054292 | 0.073884 | 0.210615 | -0.62414 | 0.38222 |
pedicel | -0.190591 | 0.359369 | 0.027441 | -0.371378 | 0.117906 | 0.37528 | 0.15697 |
P. megalanthum varieties | FA1 (25.2%) | FA2 (23.4%) | FA1 (21%) | FA2 (19%) | PC1 (29.5%) | PC2 (19.1%) | |
g~r | gr | g~r | gr | g~r | gr | ||
flower | 0.392436 | 0.664925 | 0.745911 | 0.264933 | 0.7282 | 0.25664 | |
calyx | 0.16657 | 0.885112 | 0.614819 | -0.08418 | 0.69691 | 0.57051 | |
calyx tube | 0.68603 | 0.446127 | 0.535314 | 0.386092 | 0.81223 | -0.09975 | |
lower tooth | -0.425283 | 0.725083 | 0.318941 | 0.092851 | 0.14083 | 0.82872 | |
stipules | 0.091589 | 0.427999 | -0.043631 | -0.156071 | 0.34545 | 0.26877 | |
petioles | -0.003729 | -0.36035 | 0.279887 | 0.927344 | -0.23466 | -0.27349 | |
leaflets | -0.602025 | -0.244695 | -0.361722 | 0.823352 | -0.61834 | 0.19993 | |
bracts | 0.805107 | -0.091753 | 0.188143 | 0.265238 | 0.55739 | -0.58816 | |
peduncle | 0.465463 | 0.074153 | -0.493267 | -0.003841 | 0.40407 | -0.24265 | |
pedicel | -0.672394 | 0.057123 | -0.538243 | -0.170644 | -0.47806 | 0.47628 |
Rank order of relative discriminatory power of characters for distinguishing species as ascertained by stepwise discriminatory analysis. F-ratio and probability are calculated based on the stepwise inclusion into the set of characters ranked previously.
All specimens | MVP only | P. megalanthum varieties | |||||||
---|---|---|---|---|---|---|---|---|---|
rank | Character | F-ratio | Prob>F | Character | F-ratio | Prob>F | Character | F-ratio | Prob>F |
1 | calyx tube | 156.911 | 0.0000 | bracts | 66.759 | 0.0000 | flower | 9.19 | 0.0050 |
2 | bracts | 28.938 | 0.0000 | flower | 25.432 | 0.0000 | leaflets | 2.32 | 0.1385 |
3 | flower | 13.322 | 0.0000 | pedicel | 12.814 | 0.0000 | lower tooth | 1.711 | 0.2015 |
4 | leaflets | 5.107 | 0.0009 | peduncle | 10.466 | 0.0001 | bracts | 1.299 | 0.2643 |
5 | pedicel | 3.527 | 0.0098 | calyx tube | 4.649 | 0.0128 | calyx | 1.957 | 0.1737 |
6 | peduncle | 3.769 | 0.0068 | stipules | 3.539 | 0.0345 | petioles | 0.144 | 0.7072 |
7 | stipules | 3.497 | 0.0103 | petioles | 1.543 | 0.2213 | peduncle | 0.062 | 0.8055 |
8 | petioles | 1.681 | 0.1607 | leaflets | 1.339 | 0.2690 | calyx tube | 0.052 | 0.8215 |
9 | lower tooth | 1.445 | 0.2252 | calyx | 1.475 | 0.2363 | stipules | 0.009 | 0.9257 |
10 | calyx | 2.015 | 0.0986 | lower tooth | 0.722 | 0.4897 | pedicel | 0 | 0.9864 |
Species recognition often relies on deciphering nonoverlapping patterns in morphology between biological entities (
Relationships among the species or varieties of the Pediomelum megalanthum complex have been debated among botanists, largely due to differing opinions as to which morphological characters are most important for distinguishing species. In his key to species of Pediomelum,
The morphometric analyses conducted herein largely support the use of flower and calyx sizes as being useful characters for species delimitation. All level 1 morphometric analyses involving all species in the complex, P. mephiticum, P. verdiense, P. pauperitense, and the two varieties of P. megalanthum, illustrated a clean break in overall morphological variation between P. mephiticum, P. verdiense, and P. pauperitense (the MVP group) and the P. megalanthum varieties (HCA1, PCA1; Figs
In most analyses, floral characters separated species with the greatest discriminatory power along the first component or axis of the analysis, whereas the suite of vegetative characters contributed more to the second component divisions (Fig.
The distinction of large and small flowered forms within the megalanthum complex has been recognized by previous researchers (
That said, there is some quantitative morphological and geographic separation evident between P. m. var. megalanthum and P. m. var. retrorsum. The varieties are fairly distinct geographically, with megalanthum primarily of eastern Utah, western Colorado, and northwest New Mexico and retrorsum of southern Nevada, northwestern Arizona, and sporadically along the Gila River drainage elsewhere in Arizona. Flower length was the only character having significant discriminatory power in the stepwise discriminant analysis (SDA3; Table
I agree with Grimes’ conclusions to a point with the recognition of P. m. var. megalanthum and P. m. var. retrorsum. However, after careful comparison of the character ranges of P. m. var. epipsilum with the others as ascertained by Grimes, I find sufficient distinguishing characters that separate P. epipsilum from the other varieties, including having leaflets smaller and glabrate above or sparingly strigose along veins (vs. leaflets larger and pubescent above and below in vars. megalanthum and retrorsum), and bracts larger and caudate (vs. smaller, acuminate, acute, or shortly caudate in the others). Indeed, Grimes’ quantitative character comparison shows non-overlapping ranges for leaflet and bract size, separating P. epipsilum from the others.
During an examination of Pediomelum in Arizona,
Furthermore,
The multivariate morphometric analyses on the MVP group only (level 2 analyses) were very telling. There seems to be a distinct separation between P. mephiticum and the other two species, as evidenced by all methods applied herein, but strong overlap between P. verdiense and P. pauperitense. This is perhaps best illustrated by the hierarchical cluster analysis (HCA2) which shows two main clusters, one cluster almost entirely of P. mephiticum and a second main cluster mostly comprised of P. verdiense and P. pauperitense (Fig.
As in the case with the P. megalanthum varieties, canonical discriminant analysis (Fig.
Given the overlap in continuous character distributions between several species or taxa in this study, some researchers may invoke hybridization as one reason behind overlapping morphology. Traditionally, hybridization is said to create morphological intermediacy (
Taken together, the results of this study argue for the recognition of P. mephiticum and P. verdiense at the specific level, but do not support P. pauperitense as its own species. Some researchers might suggest that P. pauperitense be recognized as a variety of P. verdiense based on geographic separation, differences in peduncle length relative to petiole length, or flower color. However, given the few numbers of populations and specimens relegated to P. verdiense and P. pauperitense, I deem it premature to make this distinction, especially considering the lack of any non-overlapping quantitative morphological character to justify this separation.
Now, with all this said and done, I revisit the initial question posed to myself: where do I lie on the spectrum of lumpers vs. splitters? Considering my conclusions in the paragraph above, I think me a lumper – at least in the case of Pediomelum. And yet, my initial inclination – prior to this analytical undertaking – was to synonymize both P. verdiense and P. pauperitense under P. mephiticum. This exercise convinced me to do otherwise – to recognize P. verdiense at the species level. This is more leaning towards a splitter mentality. The problem? Not knowing the dimensions of the spectrum! I guess I lie somewhere in the middle…
Given the conglomeration of past research with current findings shown herein, I support the recognition of P. megalanthum as having varieties megalanthum and retrorsum. I also recognize the specific status of P. mephiticum. As per the sinking of P. pauperitense under P. verdiense, a new description of P. verdiense is given below, along with a key to the taxa investigated or discussed herein.
1 | Calyx tube less than 5.5 mm long | 2 |
2 | Bracts (7–)8–12.5 mm long; calyx tube 2.5–4 mm long; plants of sw UT, nw AZ, se NV | P. mephiticum |
2' | Bracts (3–)4–8(–9) mm long; calyx tube (3.5–)4–5.5 mm long; plants of Mohave and Yavapai Cos, AZ | P. verdiense |
1' | Calyx tube more than 5.5 mm long | 3 |
3 | Bracts caudate, 13–18×6–9 mm; Upper surfaces of leaflets glabrous to pubescent only along base of veins | P. epipsilum |
3' | Bracts not caudate, or if caudate, not as large, 5–7×2.5–6 mm; Upper surfaces of leaflets pubescent throughout | 4 |
4 | Peduncle hairs shorter, appressed to incurved-ascending hairs and longer erect ones or sometimes with sparse, long curly hairs going in all directions | P. megalanthum var. megalanthum |
4' | Peduncle hairs mostly long straight erect or reflexed hairs, or rarely of short and long hairs, but then both erect | P. megalanthum var. retrorsum |
Western North American Naturalist 70: 12 (2010). Type: USA, Arizona, Yavapai Co., on the flats above a wash just north of Middle Verde exit from I-17, 18 April 2008, M. Licher 1911 (holotype BRY; isotype ASC).
P. pauperitense S.L.Welsh, Licher, & N.D.Atwood, Western North American Naturalist 70: 14 (2010). Type: USA, Arizona, Mohave Co., SW of Poverty Mountain, near Dewdrop Spring, 25 May 2001, L.C. Higgins 23135 (holotype BRY; isotypes distributed previously as P. mephiticum).
Plant acaulescent to short caulescent, 4.5–13(–15) cm tall, essentially glandular and pubescent throughout, from underground caudex branches arising from a deep, tuberous root. Stems 0–4(–6) cm, spreading white hairy; pseudoscapes 0–3, up to 6 cm, mainly subterranean; cataphylls 0–5 mm, glabrous to pubescent. Leaves clustered, palmately (3)5-foliolate; petioles 2–10(–11.5) cm long, with hairs appressed-ascending, jointed basally; stipules lanceolate to elliptic, scarious, 4–16 × 2–6 mm, tardily deciduous to persistent; petiolules 2–3 mm, pubescent; leaflet blades cuneate-obovate, (0.8–)1.2–3 × 0.7–1.8(–2.2) cm, cuneate basally, broadly acute to rounded or retuse apically, glandular and pubescent with more hairs along veins above and on lower surface, gray-green below, green to yellow-green above. Inflorescence globose, 1.5–3 cm long, with (1–)2–4(–6) nodes and (2)3-flowers per node; peduncles 0.5–4.5(–6) cm long, shorter than the petioles, spreading or spreading-ascending white-hairy, sometimes with longer spreading white hairs; bracts tardily deciduous to persistent, elliptic, 3.5–8.5(–10) × 2–6 mm. Pedicels filiform, 2.5–4.5(–6) mm long. Flowers (8–)10–13.5(–15) mm long, calyx (7.5–)8.5–12(–13) mm long, calyx-tube (2.5–)3.5–5 mm long, glandular, teeth lanceolate to oblong or elliptic, upper teeth 4–7(–8) × 1–2.5 mm, lower tooth (4–)5–9 × (1.5–)2.0–3.5 mm, gibbose-campanulate in fruit; petals white to purple, the banner white, cream, purple or suffused with pale purple, the wings and keel dark purple, with the wings sometimes lighter in color; 9–12(–14) × 6–8 mm with claw 2–5 mm, wings 10–13 × 2–3 mm with claw 4–5 mm, keel 8–10 × 2–3.5 mm with claw 3–5 mm; filaments 7–8.5 mm; anthers elliptic, 0.33 mm; ovary glabrous to pubescent apically, style concomitantly so basally. Fruits pubescent, eglandular, round to ovoid, body 5–7 × 3.5–5 mm, beak 1–4 mm, not exerted beyond calyx. Seeds oval to reniform, 3.5–5 mm × 2.5–3 mm, olive to gray brown and with or without purple mottling.
Flowering spring to summer. On limestone soils of the Verde Formation in Yavapai Co. and near Poverty Mountain in Mohave Co, Arizona.
I am grateful to the curators and staff of BRY, ASC, ARIZ, and US for use and loan of material. I am also thankful to Henrik Æ. Pedersen and Chris Puttock for helpful comments on the manuscript, as well as editor Cliff Morden and one anonymous reviewer.