Discrimination of pollen of New Zealand manuka (Leptospermum scoparium agg.) and kanuka (Kunzea spp.) (Myrtaceae)

The very similar appearance of pollen of the New Zealand Myrtaceous taxa Leptospermum scoparium s.l. (manuka) and Kunzea spp. (kanuka) has led palynologists to combine them in paleoecological and melissopalynological studies. This is unfortunate, as differentiation of these taxa would improve understanding of past ecological change and has potential to add value to the New Zealand honey industry, where manuka honey attracts a premium price. Here, we examine in detail the pollen morphology of the 10 Kunzea species and a number of Leptospermum scoparium morphotypes collected from around New Zealand, using light microscopy, SEM, and Classifynder (an automated palynology system). Our results suggest that at a generic level the New Zealand Leptospermum and Kunzea pollen can be readily differentiated, but the differences between pollen from the morphotypes of Leptospermum or between the species of Kunzea are less discernible. While size is a determinant factor-equatorial diameter of Leptospermum scoparium pollen is 19.08 +/- 1.28 mu m, compared to 16.30 +/- 0.95 mu m for Kunzea spp.-other criteria such as surface texture and shape characteristics are also diagnostic. A support vector machine set up to differentiate Leptospermum from Kunzea pollen using images captured by the Classifynder system had a prediction accuracy of similar to 95%. This study is a step towards future melissopalynological differentiation of manuka honey using automated pollen image capture and classification approaches.