A Cladistic Analysis of Iris Series Californicae Based on Morphological Data

Abstract

A cladistic analysis of Iris included 18 ingroup taxa from series Califorcticac' and two outgroup taxa from series Sibiricac'. The analysis resulted in three most parsimonious trees of 78 steps, one of which had the topology of the strict consensus tree. Twenty-nine morphological, binary and multistate characters allowed resolution of 14 monophyletic clades. The long floral tube and short floral tube groups in series Ca7lifornicac', that have been informally proposed by previous workers were found to be polyphyletic as presently circumscribed. Iris tc'niax is polyphyletic and 1. alartzvegii may be paraphyletic as currently delineated. The inclusion of taxa of proposed hybrid origin (I. halrtzvegii subsp. pim'tlorium I. Ii. subsp. columbialnaia and 1. tlhotmpsoiiii) did not increase the homoplasy present on the morphology based tree nor did it effect the analysis outcome. The inclusion of a taxon proposed to be involved in introgressive hybridization (I. piirdy/i) increased the amount of homoplasy present but did not alter tree topology. Iris is a cosmopolitan genus of perennial herbs with a northern, temperate distribution. The genus is large with more than 260 species included in a recent publication by The Species Group of the British Iris Society (1997). Iris series Califoriuicae comprises approximately 18 taxa that are distributed along the Pacific Coast in Washington, Oregon and California (Table 1). Most of the taxa within the series are found in open forests or at forest edges. Included are xeric habitats with pine in the Sierra and oak/madrone in the Klamath Mountains, and more mesic habitats with douglas fir in western Oregon and coast redwood in northern California. All members of series Califoriuicae are rhizomatouis geophytes with a basal fan of ullifacial leaves. Most members have narrow, almost grass-like leaves, which may be relatively thick and fibrous. One, two or rarely three flowers are borne in a flattened, monochasial cyme. The inflorescence of 1. doliglasiania is a complex cyme comprised of two to several partial inflorescences (Weberling 1989), with typically three flowers in each partial inflorescence. The fruit dehisces longitudinally along the midrib of each of three carpels (loculicidal capsule). Rhizomes are delicate, although in I. doliglasiatia rhizomes may reach a diameter of about 1 cm. All members of the series have a monobasic chromosome number of x = 20 (Simonet 1934). Foster (1937) and Lenz (1958) defined taxon boundaries within the series and suggested possible groupings of related taxa. Foster emphasized the capsule, seed, bract, floral tLbe and stigmatic lip (flap) as important differentiating characters. Lenz used 17 characters in his study, including inflorescence and floral parts, seeds, leaves and fragrance, although he considered several of these characters of limited taxonomic use. Character descriptions in Lenz's stLdy were largely based on relative or actLal size of the characters studied. The conclusions reached by these workers differ considerably. Most notable are their apparent disparate opinions on what constitutes a distinct taxon. Foster recognized a number of infraspecific taxa and one species (I. fliotlti0soiuii) that Lenz did not. In addition, Lenz (1959) grouped the taxa into two informal groups based on floral tLbe length, while Foster (1937) recognized three groupings within the series based on several morphological characters. Although Foster (1937) and Lenz (1959) proposed subgroups within series Califoriuicae, there has been no formulation of a phylogenetic hypothesis for the series. The lack of morphological phylogenetic work on the series may be due to several factors. Even though the group is relatively well known from previous stLdies, much of the data used in these stLdies emphasized quantitative differences in the size and shape of organs. This type of data is not as commonly used in phylogenetic work as are characters interpreted to be qualitative. Researchers also may have been reluctant to propose phylogenetic hypotheses for Iris series Califoriuicae because several of the recognized taxa have been proposed to be hybrid in origin (Foster 1937; Lenz 1959; Clarkson 1959). Taxa within series Califorilicae have been hybridized in the lab and possible hybrid zones between some sympatric taxa have been reported. Clarkson (1959) adopted an extreme view of the taxonomy of series Califoriuicae