Arthur R. Kruckeberg

An Essay: The Stimulus of Unusual Geologies for Plant Speciation

Though a regions climate sets the limits for a biota, geology enriches local discon- tinuity and habitat diversity. When slope, exposure, and physical and chemical properties of rock and soil are arrayed discontinuously, the opportunities for events leading to speciation can occur. Several scenarios can account for evolution in geologically diverse landscapes. They range from ecotypic differentiation and disruptive selection to saltational speciation. I draw upon evidence from microevolutionary response to heavy metals and from serpentine endemism. The western North American genus Streptanthus (Cruciferae), with a number of serpentine endemics, illustrates the possible modes of evolutionary diversification on this demanding substrate. Imagine a world of life without mountains, valleys, rivers, and all the other topographic intricacies of interesting landscapes. Further, conjure up a world without a mosaic of lithol- ogies-an absence of a mix of sedimentary, metamorphic, and igneous rocks, rich in vari- ant chemical and physical attributes. Without a wealth of geological diversity, the only phys- ical variable on the planet might be the contin- uous change of climate from poles to equator. Life would then have evolved a dull contin- uum of response in its tracking of gradual cli- matic change across a monotonous landscape. But the real biosphere is rich in organic diver- sity, and much of that diversity, I contend, comes form the wealth of geologic phenomena, expressed through time and space. The ingredients of the variables fashioned out of geology run the gamut from global events like plate tectonics and the drift of con- tinents to regional and local diversity created out of variant topographies and lithologies. Crucial to the argument that geological diver- sity begets biological diversity, is the realiza- tion that geological events and materials are often arrayed discontinuously. It is this discon- tinuity that sets the stage for speciation; with- out isolation, much of the worlds discrete bio- ta-as species-could not have come into being. The diversification of habitats that can flow from differences in land forms and rock types then becomes the stimulus for evolutionary di- versification by speciation. This notion can be conceptualized by paraphrasing Hans Jennys (1941) factorial equation for soil formation: s =

Ecotypic response to ultramafic soils by some plant species of northwestern United States

Soils high in magnesium derived from ultramafic rocks (serpentine, peridotite, and dunite) in northwestern United States support endemic as well as wide-ranging but edaphically indifferent(bodenvag) species. The latter occur widely on diverse rock formations of the region. Severalbodenvag species are shown to respond ecotypically to ultramafic soils. Of 18 species tested, all but three are differentiated into strains either tolerant or intolerant of ultramafic soils. Tests for edaphic preferences were conducted with seedlings and mature transplants on ultramafic soils. Growth performances were determined in greenhouse pot tests, outdoor soil bins, and by transplants in the wild. Herbaceous perennials (e.g.,Achillea millefolium, Fragaria virginiana, Prunella vulgaris, Rumex acetosella) gave the clearest ecotypic differences. Woody species either showed only slight ecotypic response(Spiraea douglasii var.menziesii andGaultheria shallon) or delayed the expression of their genotypic adaptability(Pinus contorta). Where ultramafic abut non-ultramafic soils, those populations ofbodenvag species that grow in non-ultramafic habitats can have a significant proportion of individuals tolerant to ferromagnesian soils (e.g.,Achillea millefolium). This suggests gene flow between populations of contrasting edaphic sites and possibly preadaptedness for the ultramafic habitat. Strains of two introduced weeds(Prunella vulgaris andRumex acetosella) have become ecotypically tolerant to ultramafic soils, probably within the last 75 years.

VARIATION IN FERTILITY OF HYBRIDS BETWEEN ISOLATED POPULATIONS OF THE SERPENTINE SPECIES, STREPTANTHUS GLANDULOSUS HOOK

The outcrops of serpentine and other crops). Several of these local populaferromagnesian rocks in California are tions throughout the range of the complex well known for the array of distinctive have been considered distinct enough to endemic species that their derived soils merit taxonomic recognition as species. support (Mason, 1946; Stebbins, 1942). Such a network of edaphically isolated The causal aspects of restriction to serand morphologically distinct populations pentine, the chemical basis of the edaphic poses problems in evolution and taxonendemism, the tolerance of certain plant omy that are amenable to experimental species to the low nutrient status of Caliattack. This paper presents results of fornian serpentine soils, and other ashybridizations involving thirty-two differpeets of this striking form of endemism ent population samples. Plants grown are discussed in Kruckeberg, 1951, 1954; from seed collected in the wild served as Walker, 1954, 1955; and Whittaker, 1954. the pollen and seed parents of over 300 The restriction of a number of species artificial hybrid combinations. The major of the cruciferous genus Streptanthus to effort has been to determine and evaluate serpentine soils of California has been of any correlation between the extent of spaparticular interest to students of plant tial isolation of the various populations geography and evolution (Kruckeberg, and the degree of fertility of their hybrids. 1951, 1954; Mason, 1946; Morrison, In addition, study of meiosis in many of 1941; Stebbins, 1942; Walker, 1954). the hybrids has been pursued in an atSome species of Streptanthus are found tempt to establish a cytological basis for on but one or two serpentine outcrops of the variation found in the fertility of only a few miles in extent. Others may interpopulational hybrids. show wider distribution but remain obliThis analysis of hybrid fertility thus gate to the serpentine habitat. Still others has led to an assessment of the magnimay be restricted chiefly to serpentine tudes of genetic isolation that may exist but in addition possess populations intolbetween spatially isolated populations. erant of serpentine (Kruckeberg, 1951). On the premise that degree of genetic Such facultative endemism to serpentine isolation is correlated with degree of is exhibited by Streptanthus glandulosus taxonomic relationship, the results have Hook. been applied to a taxonomic interpretaStreptanthus glandulosus, a species complex of many phenotypically distintion of the complex. Intrinsically associguishable strains, is widely distributed ated with the taxonomic objective is an throughout the Coast Ranges of central evolutionary one: To achieve an underand northern California. However most standing of the kind of genetic isolation populations are spatially isolated from that has developed during the elaboration one another due to the discontinuity of of the polymorphism exhibited by the suitable habitats (mainly serpentine outgroup.

Chemotaxonomic Diversity and Complexity in Seed Glucosinolates of Caulanthus and Streptanthus (Cruciferae)

Seed glucosinolate profiles (kinds and proportions of constituents) were analyzed by paper- and gas-chromatography for 89 collections of 40 species of Caulanthus and Streptanthus. Twenty-six compounds were identified; these are pre- sumed to be biosynthesized from five different protein amino acids. Considerable interspecific variability was uncovered, with differences involving both the number of glucosinolates constituting a profile (diversity) and the nature of biosynthetic modifications affecting their production (complexity). Serpentine-adapted taxa ap- pear to be as chemically diverse and complex as non-serpentine taxa. In general, a species possesses a characteristic chemical profile distinguishable from that of mor- phologically similar taxa. In six species significant intraspecific variability was de- tected; in S. cordatus this variability correlates with morphologically recognized infra- specific taxa. Suspected parallelism and convergence, however, reduce the taxonomic utility of glucosinolates as characters at subgeneric and generic levels in this group of Cruciferae. Caulanthus S. Wats. and Streptanthus Nutt. are two morphologically similar and presumably phylogenetically related genera of North Amer- ican Cruciferae. Together they comprise about 45 species of annual to perennial herbs that usually occupy dry, open habitats from sea-level to montane elevations. Species delimitation within each of the two and their separate generic status have been matters of long-standing controversy (cf. Payson 1923; Jepson 1925; Kruckeberg 1958; Munz 1959; Rollins 1971; Al-Shehbaz 1973; Rollins and Holmgren 1980)-an issue of some political as well as biological consequence because rare and endangered populations of these plants may be entitled to legal protection only if they constitute named taxa. As members of the putatively primitive tribe Thelypodieae, the two genera figure prominently in recent discussions on the phylogeny of Cruciferae, including place of origin and early di- versification (Al-Shehbaz 1973; Raven 1975; Hedge 1976). With the goals of testing current classifications of these genera and of describing new characters for anticipated revision and phylogenetic analysis, we initiated a paper- and gas-chromatographic survey of the glucosinolates (mustard oil glucosides) in seeds of these plants.

The Implications of Ecology for Plant Systematics

It is plant taxonomists, not taxa, that make distinctions between the formal disciplines of ecology, evolution and systematics. For populations and species in the real world, however, there is an integrating attribute: discontinuity leading to isolation. How the ecologist can contribute to the study of disjunction is the central theme of this paper. The several areas of interaction between ecology, systematics and evolution are discussed. The contribution of ecological approaches to problems in taxonomy is illustrated with recent examples in each of the following subject areas: genecology (ecotypic variation), ecology of isolating mechanisms, ecological influences on hybridization and polyploidy, ecological bases for diversification in plant genera and families, and the use of ecological data in plant taxonomy.

Manzanita (Arctostaphylos) Hybrids in the Pacific Northwest: Effects of Human and Natural Disturbance

Three species of Arctostaphylos in cismontane northwestern North America hybridize where sympatric. The combination A. columbiana x A. uva-ursi, named A. media (or A. x media), is common on disturbed forest land in western Washington and southern British Columbia. It is transient due to forest succession. The combination A. columbiana X A. nevadensis is locally common on the lower western slopes of Mt. Hood, Oregon, and adjacent southern Washington. The disturbance that may have led to the latter instance of sympatry and hybridization is less due to man than to natural causes: a mudflow on Mt. Hood dated at 1690 years B.P. Morphology, floral biology, and ecological attributes of the hybrid populations are analyzed to document the interspecific gene flow. Three species of manzanita, Arctostaphylos (Ericaceae), are found in the cismontane and coastal areas of northwestern United States and adjacent Canada-A. columbiana Piper (Hairy Manzanita), A. uva-ursi (Linnaeus) Sprengel (Kinnikinnik), and A. nevadensis A. Gray (Pinemat Manzanita). Any two of them may occur sympatrically in particular habitats. Associ- ated with the coexistence of A. columbiana with A. uva-ursi are plants of intermediate character that have been named A. media (or A. x media) (Fig. 1-3); the intermediate associated with A. columbiana and A. neva- densis has not been named. The plants named A. media Greene are un- doubted hybrids as first pointed out by Piper (in Greene, 1891). The present paper describes the ecological, phytogeographic, and floral bio- logical attributes of the recurrent hybridization. In particular, it em- phasizes the effects of human disturbance on the occurrence of the pu- tative hybrid A. x media.

Re-examination of the elemental composition of some Caryophyllaceae on North American ultramafic soils

A paper of Kruckeberg et al. (1993) reported the hyperaccumulation of nickel by Arenaria rubella at an ultramafic site at Olivine Bridge in the state of Washington, USA. Several aspects of the publication led the present authors to doubt the reliability of the data, leading to a reinvestigation of the behaviour of this species at this site. Extensive sampling of two species of the Caryophyllaceae, A. rubella and Cerastium arvense, was then carried out at Olivine Bridge in two different years, together with the collection of soil samples. The plant samples were treated in various ways in an attempt to reduce the potential influence of soil contamination. The results of this work indicate that A. rubella and C. arvense both behave in a normal way in respect of their nickel uptake from ultramafic soil. The elements nickel, iron, cobalt, chromium and magnesium have been found at levels only 1/10–1/100 of those reported in the earlier work. The weaknesses in the earlier study have led to a consideration of several aspects of putative nickel hyperaccumulation, especially as applied to species in the Caryophyllaceae. Particularly important are washing procedures, selection of material for analysis, and the use of various criteria for assessing the likelihood of soil contamination of plant samples. A careful re-examination of several other reported cases of nickel hyperaccumulation by members of the Caryophyllaceae is now recommended.

Serpentine and Its Vegetation: A Multidisciplinary Approach

Part I: Serpentine ecology. Introduction. The nature, occurrence and composition of ultamafic rocks. The formation and composition of serpentine soils. The serpentine factor. Serpentine and agriculture. Plant evolution and serpentine. Animals and serpentine. The distribution and phytochemistry of plants which hyperaccumulate nickel. Kimberlites, carbonatites and their vegetation. Part II: Serpentine vegetation of the world. Introduction to Serpentine vegetation of the world. North America. Tropical America. Northwest Europe Central and southern Europe. Continental Asia. Japan. Africa. The Malay Archipelago. New Caledonia. Australia. New Zealand.

California Serpentines: Flora, Vegetation, Geology, Soils, and Management Problems.

List of Illustrations List of Tables Acknowledgments Abstract Introduction 1. History of Botanical Observations on the Serpentine Flora of California 2. Geology of Serpentine and Related Ultramafic Rocks 3. Serpentine Soils and the Mineral Nutrition of Plants 4. Physiological and Morphological Responses to Serpentine 5. Serpentine Vegetation in California 6. Serpentine Flora in California 7. Serpentine Fauna in California 8. The Evolutionary Ecology of Serpentine Biota in California 9. Exploitation of Serpentine and Other Ultramafics and Effects on Plant Life 10. Land Management and Conservation on Ultramafics Summary Appendices Literature Cited Plates

Location and housing of institutional herbaria in The United States and Canada

:Early in 1959, C. L. t t i t cheock a n d I c i r cu l a t ed a que s t i onna i r e to most of the herbaria in the United States and Canada. The intent was to poll opinion on 1) the present , loca t ion of the h e r b a r i u m and 2) the most des i rab le loca t ion of the h e r b a r i u m , both w i th in the f r a m e w o r k of those i n s t i t u t i o n s which teach and conduc t r e sea rch in severa l fields of bo tany . The r e su l t s of th i s pol l m a y be of pa s s ing i n t e r e s t to some a n d of p o i g n a n t concern to others. To those bo tan i s t s who m a y be con f ron t ed wi th the d i l e mma of hav ing to choose a site for the i r h e r b a r i u m , the fo l lowing s u m m a r y m a y offer bo th p r e c e d e n t and gu idance in r e a c h i n g a d e c i s i o n o r in in f luenc ing the decis ions of others. Of the 118 ques t ionna i r e s sent out to i n d i v i d u a l t axonomis t s , 94 were comp l e t ed and r e t u r n e d . A l t h o u g h a few of the r e t u r n s r e p r e s e n t op in ions of di f f e ren t t axonomis t s a t the same ins t i t u t ion , most r e t u r n s sample the op in ion of a s ingle t a x o n o m i s t a t a n y one in s t i t u t ion . Thanks a re due Mr. F r e d H e d g l i n for his ass is tance in t a b u l a t i n g the resul ts . To al l those who took the t ime to fill out and r e t u r n the ques t ionna i re , we hope t ha t the p u b l i c a t i o n of the r e su l t s serves as a m o d i e m n of r eward . The ques t i onna i r e was p r e f a c e d b y the ensu ing s t a t e m e n t s :