Garcinia, , Richards, 1990

Nazre, M., Newman, M. F., Pennington, R. T. & Middleton, D. J., 2018, Taxonomic Revision of Garcinia Section Garcinia (Clusiaceae), Phytotaxa 373 (1), pp. 1-52 : 11-12

Agamospermy in Garcinia

In theory, agamospermous progeny will have a similar morphology to the mother tree and can be regarded as ‘seed clones’ ( Richards 2003). If one (or more) siblings reproduce sexually, the progeny will show some variation via increased heterozygosity. The role of agamospermy in Garcinia is not fully understood because breeding and cytology have not been studied in sufficient species. In G. celebica, Richards (1990b) observed that two populations, coastal and montane, varied in the size of the pollen, with the coastal populations having pollen grains of smaller size. It is unclear whether this variation reflects agamospermy or environmental factors.

Garcinia is the only agamospermous genus in which both sporophytic agamospermy (adventitious embryony) and gametophytic agamospermy (probably a mitotic diplospory) coexist, having evolved independently within the same genus ( Ha et al. 1988). In the presence of male plants, a substantial proportion of sexual seed formation will occur in most species (facultative agamospermy) and only in G. mangostana var. mangostana has it been suggested that there is obligate agamospermy where males are always absent ( Richards 1990a). In order to test the occurrence of agamospermy in Garcinia , simple experiments have been done by bagging the flower buds at a similar stage of development, either with the anthers (if present) removed or not ( Lim 1984). Another method involves monitoring the embryological development when no viable pollen is produced and the embryo is non-zygotic ( Ha et al. 1988, Soepadmo 1989). However, for Garcinia, Richards(1990a) outlined five criteria to determine presence of agamospermy; a) the occurrence of viable seed in the absence of pollen or after bagging flowers; b) the precocious development of the embryo before anthesis; c) the occurrence of adventitious proembryos, budding vegetatively from nucellar or integumental tissues; d) multiple seedling production from a single seed; e) a rarity or absence of males. Following these indications, Richards (1990a) listed 10 species of Garcinia that he considered agamospermous by meeting one or more of these criteria. Of these, three species are in Garcinia sect. Garcinia and their embryology has been studied: G. mangostana var. mangostana ( Lim 1984, Richards 1990a), G. penangiana (mistakenly identified as G. malaccensis ; Ha et al. 1988) and G. celebica ( Richards 1990 a, 1990b).

Using the final criterion of Richards, Thomas (1997) suggested that in Garcinia , if a species shows a female biased sex ratio, it is probably a facultative agamosperm. If this assumption is a good indication of the presence of agamospermy, then nearly all species in Garcinia sect. Garcinia may be agamospermous. This is based on the observation of the herbarium specimens in this study which shows female-biased ratios for example in G. mangostana var. malaccensis (four male out of 30 collections), G. diospyrifolia var. diospyrifolia (three male out of 33 collections) and G. nitida (two male out of 13 collections). However, Richards (1990a) stressed that more information needs to be gathered to discover whether low male ratios are truly clear indications of facultative agamospermy and the possibility that female plants are more apparent to collectors should also not be ruled out. The potentially widespread nature of agamospermy in Garcinia sect. Garcinia has been taken into account when interpreting morphological variation, and in delimiting species.