Endosperm cells contain two copies of the mother's chromosomes but only a single set of paternal genes, donated by the pollen. This so-called triploidy is a major enigma in germination biology. Moreover, species with well-developed endosperm should have lower rates of seed loss caused by sibling murder. In a review of over a thousand species of plants, Uma Shaanker's team found that in species where the endosperm is less well developed, such as orchids, legumes and wild radish, there is indeed a high incidence of seed abortion. Moreover, species with several ovules, such as the castor-oil plant and maize, tend to have a better developed endosperm than those with only one.
Some researchers remain sceptical about the idea of family conflict in plants.
Brenda Casper of the University of Pennsylvania in Philadelphia believes there is often no real conflict between seeds and their parents. Casper has found that in neotropical flora, single-seededness is closely related to the design of the fruit. Indehiscent fruits such as mangoes, which do not open to release their seeds, are more likely to produce a single seed. She argues that as fruits are maternal tissue, single-seededness is likely to be under maternal control. If sibling rivalry plays an important role, then why aren't there more examples of ovule abortion leading to single-seededness in fruits that open, she asks.