Diversity of Brassica (Brassicaceae) species naturalised in Canterbury, New Zealand

Field surveys were undertaken of Brassica naturalised in Canterbury, investigating taxonomic diversity, morphological variation, distribution, and abundance of naturalised taxa, crop escapes, and crop-weed hybrids. As a result, six species, nine varieties, and two natural hybrids were recognised as naturalised in Canterbury. B. rapa var. oleifera was the most common taxon, while B. rapa var. chinensis, B. rapa var. glabra, B. rapa var. rapa, B. napus var. oleifera, and B. oleracea var. acephala were less abundant and generally occured in small populations of only a few individuals in rural areas. Single plants of B. oleracea var. gongylodes (kohl rabi) and B. napus var. napobrassica (swede) were collected. An additional species, B. juncea, is recorded as a new naturalised plant in Canterbury. Most of the Brassica populations sampled were small, with 64% of the 107 populations observed comprising fewer than 10 plants. Flow cytometry profiles were obtained for 168 samples of B. juncea, B. napus, B. oleracea, and B. rapa, and these usually confirmed morphological identifications to a particular species. However, there were some identification uncertainties with B. napus, as some plants had a flow cytometry profile of that species but the morphology of either B. rapa var. oleifera or B. oleracea var. acephala. Tetraploid plants of B. rapa (var. chinensis, var. oleifera, and var. rapa) and B. oleracea var. acephala were recorded. We also identified two instances of hybridisation. One plant has a flow cytometry profile and a high percentage of malformed pollen that are consistent with being the putative interspecific F₁ hybrid B. napus x B. rapa. Another population included plants of the putative intraspecific hybrid B. rapa var. oleifera x B. rapa var. chinensis growing with the two parental species.