Nearly a century has been spent collecting and preserving genetic diversity in plants. Germplasm banks-living seed collections that serve as repositories of genetic variation-have been established as a source of genes for improving agricultural crops. Genetic linkage maps have made it possible to study the chromosomal locations of genes for improving yield and other complex traits important to agriculture. The tools of genome research may finally unleash the genetic potential of our wild and cultivated germplasm resources for the benefit of society.

http://www3.botany.ubc.ca/rieseberglab/plantevol/Tanksley%201997%20Seed%20banks%20and%20molecular%20maps.pdf

Seed Banks and Molecular Maps: Unlocking Genetic Potential from the Wild

Glossary of pollen and spore terminology

▪ Abstract Floral evolution has often been associated with differences in pollination syndromes. Recently, this conceptual structure has been criticized on the grounds that flowers attract a broader spectrum of visitors than one might expect based on their syndromes and that flowers often diverge without excluding one type of pollinator in favor of another. Despite these criticisms, we show that pollination syndromes provide great utility in understanding the mechanisms of floral diversification. Our conclusions are based on the importance of organizing pollinators into functional groups according to presumed similarities in the selection pressures they exert. Furthermore, functional groups vary widely in their effectiveness as pollinators for particular plant species. Thus, although a plant may be visited by several functional groups, the relative selective pressures they exert will likely be very different. We discuss various methods of documenting selection on floral traits. Our review of the literatur...

Pollination Syndromes and Floral Specialization

Rapid divergence and speciation can occur between populations with or without ecological differences under selection for success in intraspecific social competition-competition in which an individual must win in contests or comparisons with conspecific rivals in order to gain access to some resource, including (under sexual selection) mates. Sexual selection theory is extended to encompass social competition for resources other than mates. Characters used in social competition can undergo particularly rapid and divergent evolution owing to (1) their great importance in determining access to critical resources, (2) the absence of a limit to change (except by selection in other contexts), (3) the generation-to-generation relentlessness of selection on these traits. (4) the potential for mutually accelerating evolution of preference and attractiveness in contests involving "choice," and (5) the very large number of factors that can initiate trends, including mutation and drift leading to use of different phy...

Sexual selection, social competition, and speciation

The Evolution of Weeds

Crops and Man.

Summary Many of the diverse floral characteristics used by taxonomists in assessing relationships among taxa represent adaptations to specific pollinators or pollinating methods. Therefore, the diversity of reproductive methods that occurs within a phylad has a strong influence on the number of taxa that are generally recognized in the phylad. Such evolutionary phenomena as convergence and adaptive radiation of floral patterns influence the taxonomic status of various phylads or the relationships that are seen among them. Incompatibility systems are generally unassociated with morphological distinctions, but are of practical importance in crossing programs designed to test the presence and nature of genetic isolation between species, since an unawareness of their existence may lead to erroneous taxonomic conclusions. Similarly, unilateral incompatibility is discussed in relation to certain practicalities in hybridization programs. Morphological features associated with dioecism and heterostyly are disscussed as a generally overlooked source of potentially very useful taxonomic characters. The importance of adaptations to different pollinators as a basis of interspecific isolating mechanisms is stressed, as are the possible positive evolutionary (and taxonomic) consequences of a breakdown in this isolation. Floral and other characters associated with autogamy are discussed and examples are given where the relationships of autogamous taxa are uncertain because of their highly specialized reduced flowers. It is suggested that taxonomists should make an attempt to understand the reproductive methods of the plants with which they work, since such an understanding will strengthen the foundation upon which taxonomic judgments are made.

Reproductive biology in relation to systematics

The Evolutionary Significance of the Exine.

Among the most complex outcrossing systems in flowering plants are those in which floral heteromorphism is associated with a physiological incompatibility system. Such heteromorphic incompatibility systems can arise only as a result of strong selective pressures exerted over a long period of time. There is excellent evidence that when the selective pressures regulating the maintenance of these systems are relaxed or altered in their direction, the integrated syndrome of morphological and physiological traits characteristic of heteromorphic incompatibility may rapidly break down, usually in the direction of increased inbreeding. There are several evolutionary routes which the breakdown of heteromorphic incompatibility may follow. The diverse breeding systems of the American representatives of Oxalis section Corniculatae (Oxalidaceae) are most probably derived from an ancestral trimorphic incompatibility system. This paper presents a study of the breeding systems of several members of this group and briefly discusses the genetic and ecological circumstances leading to the development of these derivative systems. Oxalis section Corniculatae recently has been the subject of a taxonomic monograph by Eiten (1963), whose nomenclature will be followed here. As circumscribed by Eiten, the section contains 14 species of caulescent, non-bulbous, yellowor orangeflowered herbs with trifoliate leaves. Members of this section occur mostly in North and South America and the Greater Antilles, but two species are believed to have a natural amphi-Pacific range in North America and eastern Asia. TRISTYLOUS INCOMPATIBILITY AS AN ANCESTRAL CONDITION

The breakdown of trimorphic incompatibility in oxalis section corniculatae

Heterostyly refers to a relatively rare combination of morphological, physiological, and genetic mechanisms which promotes outbreeding in certain angiosperms. Under conditions where the selective forces favoring this degree of outbreeding are reduced or removed, one or all of the components of this character complex may break down with the result that inbreeding partially or almost wholly replaces outbreeding. There are numerous examples of such a breakdown of heterostyly in the direction of increased selfpollination in taxa belonging to various plant families. Because the complex combination of floral mechanisms and incompatibility characteristic of heterostylous plants is apparently generally effective in promoting outbreeding, the breakdown of heterostyly in the opposite direction, namely in the direction of increased outbreeding, is uncommon. Nevertheless, there is evidence that in at least two angiosperm families (Rubiaceae and Menyanthaceae) heterostyly has been replaced by an even more effective outbreeding mechanism in the form of dioecism. The purpose of this paper is to discuss the breeding systems of various distylous and dioecious members of the menyanthaceous genus Nymphoides and to present an account of the probable origin of dioecism in this genus. Nymphoides has an almost cosmopolitan distribution, occurring primarily in tropical and subtropical areas but also in certain temperate regions of both the Northern and Southern hemispheres. The plants are aquatic or subaquatic, and are typically limited to the still water of ponds, lakes, and slow-moving streams. In all Nymphoides species examined, maturation of floral buds is underwater. In the morning of anthesis the buds are raised above the water level and flowering occurs. After a few hours the corolla withers, the pedicel deflects, and subsequent fruit development is underwater. DIOECIOUS SPECIES Dimorphic heterostyly is widespread in the genera of Menyanthaceae, but dioecism seems to have been previously unrecorded for this family (Gilg, 1895). The two species of Nymphoides indigenous to the United States are dioecious. These are N. cordata, an inhabitant of ponds and slow streams ranging from eastern Canada to Florida and Louisiana, and N. aquatica, a species of similar habitats ranging from New Jersey to Florida and Texas. The two species are closely related but are distinguishable on foliar, root, and floral characters. The floral morphology of these dioecious species is very similar. The ovary of pistillate flowers is capped by a short style and a large fleshy stigma. The vestigial stamens of such flowers are relatively large and conspicuous, consisting of white anthers and short filaments. Alternating with these non-polliniferous stamens are staminode-like clusters of yellow trichomes (Fig. 1). The yellow corolla bases and additional tufts of yellow trichomes at the basal petal margins provide additional color contrast to the white corollas. Staminate flowers have well-developed stamens that produce copious pollen. The pistil of such flowers essentially lacks a style or stigma, but the ovary is large and is filled with ovules of approximately the size and number of those produced by pistillate flowers (Fig. 1). Nevertheless, despite repeated polli-

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1966.tb03368.x

Robert Ornduff

Papers

Crops and Man.

Reproductive biology in relation to systematics

The Evolutionary Significance of the Exine.

The breakdown of trimorphic incompatibility in oxalis section corniculatae

The origin of dioecism from heterostyly in nymphoides (menyanthaceae)