“…All three possible hybrid combinations have been reported, but it is doubtful whether the tetraploid hybrid between P. reptaris and P. erecta actually occurs in nature (Matfield, 1972). It has recently been synthesised experimentally (Schwendener, 1969;Matfield, 1972) but previous attempts to hybridise the tetraploid species failed as a result of genetic incompatibility barriers (Brukss, 1931;Matfield, Jones and Ellis, 1970). For this reason confirmation of the allopolyploid origin of P. anglica by experimental synthesis has proved difficult.…”