Apomixis

The setting of seed without fertilisation. The seed inherits as its mother did, so even a hybrid's offspring do not split. It occurs in the hawkweeds Mendel turned to after his peas.

To see whether his pea rules held for other plants, Mendel crossed hawkweeds (Hieracium). In a letter of 1870 he wrote that their hybrids behaved in exactly the opposite way to the peas, breeding true in the next generation. In 1873 he reported that in orange hawkweed (Hieracium aurantiacum) and others, even after cutting away the tube that sheds pollen and applying pollen from another species, he raised only plants like the mother, and he put this down to the plant's own pollen getting there first^[1].

The reason became clear only after his death. In 1904 the Danish botanist C. H. Ostenfeld reported that many hawkweeds set seed without fertilisation^[2]. If the pollen plays no part, the pea rules cannot show. The second plant Mendel chose to test his rules turned out to lie outside them.