Taximetrics as Applied to the Genus Lithophragma (Saxifragaceae)

Abstract

A taximetric analysis of Lithophragma, a genus endemic to North America containing 10 taxa, reveals a close similarity to the taxonomy proposed by the author in a recent monograph using the traditional intuitive approach. The taximetric method is based on a neo-Adansonian approach utilizing the same characters used in the intuitive study, but arbitrarily giving equal weight to all unit characters. A total of 29 unit characters was employed and although this is fewer than is considered necessary by most taximetrists to ensure reproducible results, the analysis is restricted to but a single small genus. The number of unit characters could be greatly increased by the inclusion of generic characters; however, such characters would be merely redundant and positive. A rearranged similarity matrix and dendogram are included. The conclusion is reached that taximetrics may help place plant taxonomy on an objective basis as is classification ill such disciplines as physics and chemistry. Its application, however, must await extensive documentation of plant taxa on a broad basis. 1

Ecological studies of polyploidy in the 100 years following its discovery

“…There are counterexamples to these trends. For example, polyploidy occurs in some groups of primarily or obligately outcrossing plants-including annuals and perennials without vegetative reproduction [96,102,103,106,108]and some polyploids have small geographical ranges or scattered distributions [26,73,110,111,128]. To our reading, however, correlates of polyploidy reported by biosystematics seem believable and worthy of further investigation.…”

“…For example, multiple origins of polyploid taxa are well known today based on analyses of DNA sequence data and molecular markers (isozymes, restriction fragment length polymorphisms, microsatellites, etc. ), but during the biosystematics era were inferred on the basis of disjunct geographical or ecological distributions [110,111], morphological or karyotypic divergence among polyploid populations [112][113][114], and the occurrence of unreduced gametes in wild populations [108,115].…”

“…By contrast, autopolyploids were regarded as rare and evolutionarily much less significant. Because of the morphological similarities between diploids and autopolyploids-and potential for gene flow via triploid F 1 hybrids and unreduced gametesthere was general disinterest in naming autopolyploids, even among the few biosystematists who thought they existed frequently in nature [99,[111][112][113]116]. Thus, Harlan Lewis [26] (who investigated autopolyploidy in Delphinium and allopolyploidy in Clarkia) wrote 'on no grounds .…”

“…Because polyploidy is ostensibly more common in arctic and north temperate floras than in the tropics [2,3,69,88], recognition of chromosome races may alter latitudinal and geographical patterns of plant biodiversity. Finally, there are many instances of rare cytotypes (geographically restricted or sparsely distributed) in polyploid complexes that are otherwise common [15,26,106,110,111,128,285]. Recognition of these cytotypes at the specific or subspecific level may influence formal protection under the law and is probably warranted given their biological attributes [158,286].…”

Evaluating the Dynamics of Coevolution Among Geographically Structured Populations

“…Traditionally, the Lithophragma populations have been divided into as many as nine species (Taylor 1965), but the molecular data (and associated morphological and ecological data) suggest that there are two species groups with indistinct species limits among populations within those groups. The L. parviflorum complex (L. parviflorum/affine/tenellum/trifoliatum) is a monophyletic geographic cluster of closely related populations.…”