December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Section Diphysi from other putatively related sections.
The thickness or texture of the valve walls, the type and
distribution of pubescence on the valves, and the degree
of closure of the locules by the septum (if it is complete
and fused to the funicular flange throughout or just
within a portion of the body of the pod) is highly variable
throughout the range of this species.
The second group within this complex is characterized
by having scarcely inflated (cylindrical to ventricose
in shape and slightly inflated dorsally, if at all),
thick papery to leathery, elliptic, narrowly oblong, to
linear pods. The septum is generally incomplete in this
group, either semi-bilocular (the septum partially divides
the two locules) or sub-unilocular (the septum is
less than half the width of the locule). Unlike the first
group, the pods are either deciduous or long-persistent.
These scarcely inflated taxa were first comprehensively
described by Rydberg (1929) as Section Palantia
Rydb. within the genus Tium Medik., based on the similarity
of the pod morphology. The remaining members
of Section Diphysi were split and included in the old
world genus Cystium Steven. The degree to which these
characteristics define a section or species is a major
source of disagreement among all monographs of this
complex (Barneby 1945, 1964, Isely 1998, Jones 1923,
Rydberg 1929, Welsh 2007). The long-persistent pods
in one taxon, A. lentiginosus var. mokiacensis (A. Gray)
M.E. Jones, was the primary character that lead Barneby
(1989) to retain it within the Section Preussiani M.E.
Jones, a section distantly related to Section Diphysi.
Vastly different interpretations of the significance of
this character have led to often disparate views of the
species boundaries and delimitations surrounding these
taxa (Alexander 2005, Barneby 1964, 1989, Welsh
2007). When the taxa with persistent pods are delimited
as varieties, Astragalus lentiginosus becomes the only
documented North American species of Astragalus to
have forms with both persistent and deciduous pods.
All other examples proposed by taxonomists have been
split at the species or the sub-sectional level in recent
monographs.
In the most recent revision, Alexander (2008) considered
all of the scarcely inflated varieties of A. lentiginosus
to be a single evolutionary lineage and referred to
them collectively as the Palantia, based on Rydberg's
sectional name. The Palantia consists of A. lentiginosus
var. bryantii (Barneby) J.A. Alexander, A. lentiginosus
var. iodanthus (S. Watson) J.A. Alexander, A. lentiginosus
var. maricopae Barneby, A. lentiginosus var.
mokiacensis (including A. lentiginosus var. trumbullensis
S.L. Welsh & Atwood), A. lentiginosus var. palans
(M.E. Jones) M.E. Jones, A. lentiginosus var. pseudiodanthus
(Barneby) J.A. Alexander, A. lentiginosus var.
ursinus (A. Gray) Barneby, and A. lentiginosus var. wilsonii
(Greene) Barneby. The name, Palantia, is not used
herein in a nomenclatural sense as a sub-generic or sectional
name. It is unusual in botany for a collective
name to be required for clarity when referring to groups
of morphologically similar varieties. However, with
over 40 varieties and 4 or 5 lineages that are similar
morphologically, a collective naming convention for A.
lentiginosus is necessary to refer to these groups. As
such, the Palantia is used as a convenient, informal
name for the varietal group with scarcely inflated pods
and is italicized following the common literary convention
for unfamiliar Latin words.
Within the Palantia, two taxa, Astragalus lentiginosus
var. maricopae and A. lentiginosus var. ursinus have
been historically overlooked by taxonomists and have
an uncertain taxonomic status. Astragalus ursinus A.
Gray (first reduced to a variety of A. lentiginosus by
Barneby 1964) was the first to be described in 1878,
along with A. mokiacensis A. Gray (Gray 1878). Gray
was the first to propose a close relationship between
these taxa and A. lentiginosus var. iodanthus (at that
time, and until only recently, this taxon was delimited as
a species). The affinity of the types of A. ursinus to extant
populations has been controversial since the taxon
was first described (Alexander 2005, 2008, Barneby
1964, Jones 1923, Welsh 1978, 2007, Welsh & Atwood
2001). In some recent taxonomic treatments (Barneby
1989, Welsh 1993), the types have been regarded as an
insignificant variant of A. lentiginosus var. palans.
However, in others A. lentiginosus var. ursinus is recognized
as an insignificant variant of A. lentiginosus var.
mokiacensis (Alexander 2005, Welsh 2007, Welsh &
Atwood 2001).
Based on a combination of field surveys, morphometric
analyses and chloroplast haplotype analyses, Astragalus
lentiginosus var. ursinus was found to be genetically
distinct from its geographically closest relative,
A. lentiginosus var. mokiacensis (Alexander 2008, Alexander
& Liston, in prep). In addition, Astragalus lentiginosus
var. ursinus is a highly restricted limestone talus
endemic (totaling less than 5,000 individuals), and is
confined to a small region of the Beaver Dam Mountains
in Mohave County, Arizona and Washington
County, Utah (Alexander 2008).
The second species, Astragalus lentiginosus var.
maricopae, was first described in Barneby's (1945)
monograph. It is often confused with A. lentiginosus
var. yuccanus due to similar floral morphology (size and
color) and has remained poorly known since it was first
described. The floral and pod morphology are highly
distinct when compared to the other members of the
Palantia. If it were placed within any other section of
the genus, it would be recognized at the species-level. It
has universally been recognized as a variety of A. lentiginosus
in all major monographs, but has only recently
been found to be a restricted endemic (Alexander 2008).
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