When a classification based upon certain morphological and physiological characters of the stigma was applied to ca. 1,000 species of some 900 genera of angiosperms, several taxonomic regularities emerged. Most families proved to be relatively homogeneous in stigma type, whilst others were strikingly diverse. Among the latter were certain supposedly primitive families such as the Liliaceae, a fact that may have some phylogenetical significance. Sometimes where a family proved to be homogeneous in respect to the more general characters of the stigma, fuller investigation revealed great variation in detail. An example is given by the Boraginaceae, a family in which stigma characters are of potential taxonomic importance. The stigma papillae in this family are often capitate, with heavily cutinised heads, and pollen has to be inserted forcibly between the papillae. There is a strong correlation between pollen size and stigma–papilla size, so that certain types of cross pollination are impossible. These specialisations can thus play a part as isolating mechanisms. The form of the stigma papillae is probably also important in genera of the Boraginaceae adapted to arid conditions, since the contiguous cutinised caps overarch the actual receptive surfaces and so. presumably, offer protection from desiccation.

In both monocotyledons and dicotyledons, clear relationships exist between stigma type and physiology, and notably with the type of self–incompatibility system. It is already apparent that stigma characters can have predictive value in the investigation of breeding systems.

The paper includes a comprehensive literature list, covering most ot the principal sources of structural, taxonomic and other data bearing upon angiosperm stigmas.

Stigma characteristics and angiosperm taxonomy

HXSTORaC^L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472 VxscuLAR GROUND PLAN ANY ITS MODXFICATO~r . . . . . . . . . . . . . . . . . . . . . . 476 Typica l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 Modificat ion by Reduct ion . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476 Modificat ion by Cohesion and Adna t i on . . . . . . . . . . . . . . . . . . . . . . . . . . 477

The role of floral anatomy in the solution of morphological problems

Placentation in angiosperms

Different approaches to circumscribe staminodial structures in the angiosperms are reviewed. The need for a morphological distinction between “true staminodes” (derived from stamens or homologous to stamens) and “pseudostaminodes” (nonhomologous to stamens) is emphasized. In phylogenetic studies the term “staminode” is often used uncritically, without knowledge of the true homology of these structures. Staminodes are either whole organs (outer tiers or whorls, namely petals, intermediate tiers, or organs within a tier), or partial organs. This article aims to discuss the shortcomings of the past and current approach of staminodes and proposes definitions of staminode types for use as characters in phylogenetic analyses. Staminodial structures should be classified according to their position and function in the flower. Both aspects are intricately linked and make the identification of staminodes sometimes problematic. Shifts in time (heterochrony) and space (heterotopy or homeosis) make that a regressing organ either aborts completely or becomes remodeled into something new. Petals are included in the definition of staminodes as they combine function and heterotopy. A hierarchical ordering of staminodial types is given and discussed. Three interdependent but possibly complementary functions are attached to the occurrence of staminodes: an attractive, nutritional, and structural function. The importance of staminodes for the evolution of the androecium and flower is demonstrated. The difficulty in unmasking pseudostaminodes, comprising receptacular disks, is demonstrated. The value and shortcomings of molecular-based interpretations of staminodes are discussed. It is shown that the decision to recognize a staminode from receptacular emergences often relies on unstable grounds and remains largely dependent on the acceptance of a given phylogenetic background.

Staminodes: Their morphological and evolutionary significance

http://www.sci.sdsu.edu/plants/cryptantha/pdfs/Cohen2013-Boraginaceae.pdf

A phylogenetic analysis of morphological and molecular characters of Boraginaceae: evolutionary relationships, taxonomy, and patterns of character evolution.

THE TAXONOMIC treatments of the Boraginaceae since the description of certain species by Linnaeus in 1773 have been many and varied. While for the most part these are regional and incomplete, even sectional treatments show clearly that the tribes and apparently many of the genera are based on tendencies and overlapping characteristics rather than clearcut differentiating characters. In a study of the detailed anatomical features of the flowers it is of interest to find whether or not these classifications based on gross morphology can be supported or clarified. The size and range of the family make it hardly to be wondered at that the taxonomic treatments are preodminantly regional. In the main, however, workers have agreed that the family is divisible into four subfamilies. A further division of one of these subfamilies into tribes is to be used in this paper. In order that the subfamilies as generally accepted be clearly understood, the following table of characteristics has been compiled from Baillon, Bentham and Hooker, Engler and Prantl, and De Candolle:

Julia Ruth Lawrence

Papers

A correlation of the taxonomy and the floral anatomy of certain of the boraginaceae