An Unusual Kind of Distyly in Quinchamalium Chilense (Santalaceae) on Volcán Casablanca, Southern Chile

Abstract

In mature flowers of the southern Andean parasitic herb, Quinchamalium chilense (Santalaceae), the stigmas and anthers are closer together in the pin morph than in the thrum morph. While the stigmas and anthers of the two morphs are in reciprocal positions as the flowers open, such reciprocity is lost as the result of post‐anthesis allometric growth of the styles and stamens. Experimental pollinations reveal that both morphs of Q. chilense are self‐compatible. Natural fruit set is higher on the pin morph. The latter is also statistically under‐represented in natural populations with respect to a 1:1 ratio for pins and thrums. Pin flowers produce larger numbers of pollen grains than thrum flowers and pollen of pin flowers is smaller in size than that of thrum flowers. Higher fruit set on the pin morph is consistent with some tendency towards subdioecious breeding behavior, although an expected excess of geitonogamous pollinations on the pin morph might also be contributing to the difference in fruit set on the two morphs. The unusual floral morphology of Q. chilense could have evolved as a result of selection for larger flowers by certain pollinator groups less likely to effect geitonogamous pollination. Alternatively, extended development of post‐anthesis flowers might be a reflection of selection for an array of flower sizes on individual inflorescences, producing a target effect for pollinator attraction. The evolution of such inflorescence morphology would have been facilitated by the fact that a trend in the direction of subdioecious breeding behavior accrues the same outcrossing advantages as strict distyly. Precise information on periods of stigma receptivity is required to further our understanding of the floral morphology of Q. chilense.

Reciprocal style polymorphisms are not easily categorised: the case of heterostyly inLithodoraandGlandora(Boraginaceae)

“…After morphological characterisation of the species, the great variation in stamen position as compared to stigma position in both subspecies of G. prostrata would suggest a new type of polymorphism, called relaxed stylar dimorphism, which is characterised primarily by wide amplitude in the height of anthers, causing low reciprocity (Figs 4 and 5). We use the term ‘relaxed’ because anthers within a flower do not present a uniform height, as in typical style dimorphic and distylous species ( e.g ., Riveros et al. 1987; Pailler & Thompson 1997).…”

Flower Development and the Evolution of Self-fertilization in Amsinckia: The Role of Heterochrony

“…From a flower developmental point of view, there are various developmental processes and modifications that can differentiate two distylous flower morphs. Changes in developmental rate, however, are usually the major cause that leads to the contrasted flower morphology of pin and thrum in distylous species (Stirling 1936;Riveros et al 1987;Richards and Koptur 1993). This must be true whenever final size differ but developmental durations do not.…”

“…Quinchamalium chilense Riveros et al 1987 and Guettarda scabra Richards and Koptur 1993). In all three distylous species of Amsinckia, the developmental rate for all stamen-height-associated traits was highly significantly slower in pins than in thrums (Table 2).…”

Comparative floral development in Lithospermum (Boraginaceae) and implications for the evolution and development of heterostyly

“…Although numerous studies (e.g., Kohn et al, 1996; Morris, 2007; McDill et al, 2009; Thomas et al, 2008; Ferrero et al, 2009; Cohen, 2011) have investigated the evolution and phylogenetic relationships of heterostylous taxa, only a limited number have examined the floral developmental patterns of heterostylous species (e.g., Stirling, 1932, 1933, 1936; Riveros et al, 1987, 1995; Richards and Barrett, 1992; Richards and Koptur, 1993; Faivre, 2000; Webster and Gilmartin, 2006; Hernández and Ornelas, 2007; Li and Johnston, 2010). Floral developmental studies, particularly when placed in a phylogenetic context, help in understanding the evolution of floral architecture, including features such as flower size and organ number (Hufford, 1988; Tucker, 1997; Faivre, 2000; Armbruster et al, 2002; Bissell and Diggle, 2008; Kirchoff et al, 2009; Li and Johnston, 2010).…”