REVISION OF ANACYCLUS 95 



remotely, Anthemis and its allies do commonly have loose cymes but exhibit a number of stem- 

 reduction trends. 



Receptacle 



The receptacle is flat or very shortly conical and is, in all species, paleate, i.e. furnished with 

 involucral bracts subtending each disc-floret. In all species these are particularly well developed, 

 in fact perhaps the most distinctive in the Anthemideae. They show considerable variation in the 

 genus, the toughest and most persistent being found in Anacydus pyrethrum and A. monanthos 

 subsp. monanthos (Figs 12, 14) and the most herbaceous in A. latealatus and A. nigellifolius 

 (Fig. 26). They also show considerable variation in shape and dimensions. In A. pyrethrum they 

 are distinctly obcuneate and almost as broad as wide with a tough mucronate acuminate apex, 

 distinctly caniculate and overtopping the ripe cypsela at maturity. In A. nigellifolius the opposite 

 extreme occurs, in that the receptacular scales are obovate-acuminate, somewhat flimsy and 

 scarious and only loosely investing the cypsela at maturity. 



Correlated with the variation in form is the strength of attachment to the receptacle. In all taxa 

 the receptacular scales and cypselas are loosely attached to the receptacle. In A. clavatus, A. 

 homogamos, and A. radiatus the scales are readily deciduous and will fall off the receptacle at the 

 same time as the involucral bracts and cypselas, after the withering of the capitulum. In A. 

 pyrethrum and A. monanthos subsp. monanthos they are persistent on the receptacle, and since 

 they overtop the cypselas, the whole capitulum is dispersed as a single diaspore. Both these taxa 

 occur in habitats with great climatic extremes, and, as a result, both have a prostrate growth 

 habit. It seems that the mature capitula of the perennial A. pyrethrum are deposited a short 

 distance away from the parental plant after it dies down for the winter, and those of the annual 

 A. monanthos are left near the site of the parent plant after it disappears altogether. 



Involucre 



The involucre in Anacydus consists of a hemispherical cup comprised of pluriseriate, brown or 

 brownish-green bracts. Although the actual dimensions of the involucre can vary enormously, 

 the shape can invariably be described as campanulate. The innermost bracts are usually obovate- 

 spathulate, e.g.in A. clavatus (Fig. 19), with a small to spreading erose apex, e.g. in A. radiatus 

 (Fig. 17). Sometimes the limb is virtually absent and the innermost bracts are oblong or triangular, 

 as in A. pyrethrum (Fig. 12) or A. maroccanus (Fig. 16). The different conditions of the involucre 

 are fairly uniform in particular species and species groups, e.g. A. radiatus. 



In the annuals the bracts are usually a more or less uniform light-brown colour, moderately 

 scarious and distinctly hairy. However, the opposite extreme conditions can be seen in A. maroc- 

 canus and A. pyrethrum, which have distinctly herbaceous, green involucral bracts with narrow, 

 dark brown margins and are usually subglabrous. 



Florets 



The floral characters of Anacydus are particularly variable, especially in the presence and absence 

 of ray florets, the size of ray florets, ray-floret colour, lobe size of the disc florets, the degree of 

 compression of the corolla tube and the shape and size of corolla-tube appendages. 



Most species are gynomonoecious with a single row of ligulate female florets and a central mass 

 of perfect, hermaphrodite disc florets. A. monanthos and A. homogamos, by contrast, are mono- 

 ecious with all the florets hermaphrodite. Robust, apparently discoid plants of northern Morocco 

 and the western European Mediterranean region sometimes have a small number of extremely 

 short female ligules, often hidden below the involucral bracts (Fig. 19). These have been considered 

 by Maire (1932) to be a polymorphic intermediate form between the ligulate and eligulate condi- 

 tions. One hypothesis to explain such variation would be that these plants represent an inter- 

 mediate stage in the evolution of the monoecious discoid head. However, data from experimental, 

 morphological and geographical studies would suggest that the heterogamous plants of A.x 

 valentinus are more likely to be hybrids between the yellow-liguled A. radiatus and the discoid 

 A. homogamos (see p. 128; Humphries, in press, a). 



