98 C. J. HUMPHRIES 



the compression of the fruit is a derived feature, then it follows that the elaboration of the wing is a 

 consequence of the reduction of the main fruit body, since the overall dimensions of the fruit 

 vary little within the genus. The transformation series is presented in Fig. 4, with the least elaborate 

 fruits in A. pyrethrum and those with the broadest wings in A. latealatus and A. nigellifolius. 



Changes accompanying the expansion of the wing include the erosion of the wing margins (as 

 exemplified by the tough spines of A. monanthos and the delicate fimbriate margins of A. maroc- 

 canus), a general correlation between area and thickness of the wing (the broader the wings the 

 more scarious they are), and an increase in pappus size associated again with increase in lamina 

 area. One important species-specific characteristic is the vertically orientated auricles in A. 

 pyrethrum, as distinct from the generally outwardly pointing auricles of the annual species. 



A feature mentioned by Grierson (1975a) is the persistence of ray corolla lobes on the cypsela 

 at maturity. Abscission of the ray corolla at the point below the ligule is frequently encountered in 

 most of the radiate species but is particularly apparent in A. nigellifolius, where it appears that the 

 corolla tube is fused with the cypsela through maturity and dispersal. 



The pappus is either absent (e.g. in A. pyrethrum) or varies from an extremely narrow, marginal 

 corona to a thin, lacerate scarious appendage contiguous with the wing auricles. 



In transverse or longitudinal section the individual parts of the cypsela, viz. the ovary wall, the 

 testa, the pericarp and the hypanthial tissue, are impossible to identify fully from anatomical 

 observations. However, it is easily possible to separate the testa from the fruit wall and consider 

 the pericarp as two layers - epicarp and mesocarp. In Anacyclus, most variation occurs as 

 modifications to the mesocarp, especially in the thickness and angle of the cells in the wings and 

 the thickness of the anterior and dorsal layers. 



The pericarp and integument are often tightly attached to one another but do not coalesce. 

 In the preparations used for Fig. 5, they are clearly seen to be separated from the fruit wall. 

 The integument in all taxa consists of two layers, an outer epidermis with lateral or U-type 

 thickenings and an inner layer of flattened, densely cytoplasmic cells. 



The ovary is supplied with two vascular bundles lying marginally in the basal part of the rib 

 (Fig. 6 B). They both divide at the base to provide two embryo traces and again at the apex, just 

 below the pappus, to form two semicircular rings of corolla and stigmatic traces. The semicircular 

 rings are asymmetrical. One of them divides three times to give one stigmatic trace and three 

 corolla traces, whilst the other divides only twice to give two corolla traces and one stigmatic 

 trace. Within the corolla tube the five corolla traces again divide near the base to give five outer 

 traces. 



Variation in the pericarp anatomy reflects to a great extent the differences in external morpho- 

 logy, the most important specific differences being the degree of sclerification of the mesocarp, 

 the thickness of the mesocarp in the region of the anterior and dorsal faces, and the relative length 

 of the wings and embryo. In all taxa the mesocarp parenchyma develops wall-thickening during 

 maturation. The sclerenchyma is mostly due to scleroid development. The degree of thickening 

 varies in different parts of the cypsela, particularly in the ribs, the faces and the apical region of 

 the fruit wall. The most obvious and most densely thickened regions in all taxa are the basal 

 regions of the lateral ribs in the portion surrounding or overtopping the vascular bundles. In 

 the majority of the annual species the anterior and dorsal faces of the mesocarp are extremely thin, 

 often only one cell thick. Nevertheless, the cells are heavily thickened to the same degree as the 

 lateral bundles. By contrast, the cells of the pericarp in A. pyrethrum are only slightly thickened 

 at maturity but are some 3-4 cells thick in the region of the faces. The epicarp epidermis is 

 invested along the margins and at regular intervals on the surfaces with myxogenic cells (Fig. 6). 



The general expansion of wing area and reduction in the main body of the fruit is associated 

 with the development of smaller cotyledons and a thinner mesocarp. 



Chromosome numbers 



Somatic chromosome numbers have been investigated in five species. All of them have 2n= 18 

 (see Humphries, in press, a and Humphries et al., 1978, for review). The four annuals which have 

 been examined, Anacyclus radiatus subsp. radiatus, A. radiatus subsp. coronatus, A.xvalentinus 

 and A. clavatus, all differ from the perennial A. pyrethrum in having three, instead of two, pairs of 



