Sexual Systems in Prunus

Transactions of the Linnean Society of London: Botany. Second ser, 1: 338 (1875)
On the self-fertilization of plants
Rev. Henslow
Lastly, Prunus spinosa and Padus, as well as Crataegus oxycantha, are proterogynous.

Heideman: Sexual Affinities of Prunus americana (1895)
We know this from the fact that distinct species will sometimes cross, but not freely, in a reciprocal direction. I have myself, within the past ten years, produced hybrids between P. angustifolia and P. Americana; between P. domestica and P. Americana; between P. Besseyi, Bailey (P. pumila Lin.) and P. hortulana, B.; between Cerasus avium var. and P. Besseyi, B. I made several hundred crosses to produce hybrids between our sand cherry (P. Besseyi) and horticultural varieties of Cerasus avium. Pollen of C. avium var. on P. Besseyi invariably proved sterile; reciprocal crosses set fruit, but they failed to germinate, the seed containing only a trace of the aborted ovule. When I finally used the pollen of a proterandrous form of P. Besseyi on a short-styled form of C. avium fertilization was effected and developed a normal fruit, the seed of which germinated and produced an undoubted hybrid. The reciprocal crosses of the same varieties failed to fertilize a single ovule out of over fifty crosses made. I had applied the same principle in the production of hybrids between P. hortulana and P. Besseyi with fair success.

Pollination in Plums (Dec 1898)
F. A. Waugh
According to my own observations the proterogynous forms are relatively common in the Western wild plum, the typical Prunus Americana, and its varieties. Proterandrous forms are infrequent and not pronounced, though Professor Sargent, who makes Prunus nigra separate from P. Americana, mentions proterandry as characteristic of that species. Long-styled forms are rather frequent, but I have not seen the short-styled forms outside Prunus Virginiana and P. serotina. The gynodioecious form I have never seen, nor any pronounced suggestion of it; though the andromonoecious form is very common both in Prunus Americana and P. Chicasa. It is only less common among varieties of the Wild Goose group, and may be found among the Japanese varieties, or even among the varieties of Prunus domestica, where it is most unusual. The Marianna plum is also often andromonoecious. A very large proportion of blossoms rated in the succeeding tables as having defective pistils, belong to this class.

Biological Journal of the Linnean Society, 50(1): 65-84 (Sept 1993)
Pollination biology of Prunus mahaleb L.: deferred consequences of gender variation for fecundity and seed size
Pedro Jordano
This study describes the reproductive biology of Prunus mahaleb, a rosaceous treelet, in a southeastern Spanish population. The species is gynodioecious with 55.4% of the plants being male-fertile and 44.6% presenting non-functional, shrunken anthers with no pollen, and behaving as functional females.

Acta Phytotaxonomica et Geobotanica 52(1): 115-124 (2001)
Dimorphic Nature in Stigma-Anther Separation of Prunus nipponica (Rosaceae)
Satoko Hirata, Takashi Sugawara
Stigma height, anther height and stigma-anther separation were studied to examine their dimorphic nature in two populations of Prunus nipponica occurring in sub-alpine zone of Mts. Norikura and Utsukushigahara, central Honshu of Japan. The stigma and anther heights considerably varied among the plants and each of the characters showed normal frequency distributions within populations. However, stigma-anther separation showed a bimodal distribution. Based on this floral character the populations concerned were tentatively divided into two discrete floral morphs: long (L)-styled morph and homo (H)-styled morph. Each of the two morphs was highly constant within a plant and did not change its floral nature for over two years. Artificial pollination experiments indicated that the two morphs were strongly self-incompatible and crosses between the same morphs (HxH or LxL) produced seeds in higher percentage. These results suggest that the dimorphic nature in P. nipponica does not exhibit an ordinary heterostyly but may be regarded as an example of herkogamous polymorphism. We briefly discuss on the possible adaptive significance of dimorphic natures of the flowers exhibited by P. nipponica.

Mol Ecol. 14(6): 1821-30. (May 2005)
Mating patterns, pollen dispersal, and the ecological maternal neighbourhood in a Prunus mahaleb L. population.
García C1, Arroyo JM, Godoy JA, Jordano P.
Gender polymorphism, plant-animal interactions, and environmental heterogeneity are the three important sources of variation in mating system and pollen dispersal patterns. We used progeny arrays and paternity analysis to assess the effects of gender type and density level on variation in mating patterns within a highly isolated population of Prunus mahaleb, a gynodioecious species. All the adult trees in the population were sampled and located. The direct estimate of long-distance insect-mediated pollination events was low (< 10%). Gender expression deeply influenced the mating system, decreasing the outcrossing rates (t(m)) and the pollen pool diversity in hermaphrodite trees. Long intermate distances (> 250 m) were significantly more frequent among female mother trees. Variation in local tree density also affected pollen pool diversity and intermate distance, with a higher effective number of fathers (k(e)) and longer intermate distances for female trees in low-density patches. A canonical correlation analysis showed significant correlations between mating variables and the maternal ecological neighbourhood. Only the first canonical variable was significant and explained 78% of variation. Outcrossing rates tended to decrease, and the relatedness among the fathers tended to increase, when mother trees grew in dense patches with high cover of other woody species and taller vegetation away from the pine forest edge. We highlight the relevance of considering maternal ecological neighbourhood effects on mating system and gene flow studies as maternal trees act simultaneously as receptors of pollen and as sources of the seeds to be dispersed.

Botany, 95(9): 913-922 (2017)
Sex morphs and invasiveness of a fleshy-fruited tree in natural grasslands from Argentina
M.R. Amodeo, S.M. Zalba
Invasiveness has usually been studied as a species-level attribute; nevertheless, phenotypic differences between individuals in a population can lead to significant variations in colonization ability. In this paper, we analyse the potential effects of sex morphs of Prunus mahaleb L., a gynodioecius fleshy-fruited tree, on its invasiveness in natural grasslands in the southern Argentine Pampas. We assessed the abundance of both hermaphrodite and female plants, and compared their fecundity, propagule size, and germination response. We found that the females were less abundant in the invasive populations studied, apparently since the beginning of the colonization. However, our results demonstrated that at the present time, females do not show any fecundity reduction, which clearly shows that P. mahaleb has established an effective interaction with generalist pollinators that compensates for the apparently disadvantaged females. Fruit set showed a wider range of variability over time in the females than in the hermaphrodites, which could be the consequence of greater susceptibility to changes in the activity of pollinators. We found no evidence of a female benefit due to reallocation of resources or better outcrossed progeny when considering propagule size and germination. We discuss the relative importance of sex morphs and interactions at different stages of the invasion process.

Prunus geniculata
The species is andromonoecious, with individuals bearing both bisexual and male-only flowers.