Grass Peas near the Sign of the Kiwi, Canterbury, New Zealand

On 19 October, iNaturalist user @joepb discovered a population of grass peas (Lathyrus sphaericus) in flower in the Coronation Reserve near the Sign of the Kiwi on the Banks Peninsula in Canterbury, New Zealand. His observation represented the first sighting of the species in New Zealand on iNaturalist, and a bit of digging at GBIF revealed that it was only the second New Zealand sighting at all since 1990, when a herbarium specimen was retrieved from very nearly the same location. Oblivious to all this, I happened across a third specimen on 2 November near where the other observations were recorded.

It was pretty cool to rediscover a species that had persisted unnoticed for nearly 30 years. We have no idea how extensive its distribution is since L. sphaericus is native to Europe and the recorded observations were all made in close proximity to each other, so on 4 November, I set out after work to see if I could find some more specimens in the Coronation Reserve. Starting from the saddle between Coronation Hill and the hill immediately south of it, I set off on the loop track around the bottom of Coronation Hill going anticlockwise. I finally found some specimens at the edge of the little wood behind the Sign of the Kiwi cafe. I found one or two more near the one I found on 2 November, next to the track adjacent to the cafe. I then found quite a few more near Joe's 19 October observation, then they petered out. I found one more small population below the walking track a little further on.

My 4 November trip was fruitful, and I'll try and summarise my perception of its distribution. L. sphaericus is not nearly as common as the little purple vetch (Vicia sativa, I think) that is found all over the place on the Port Hills, but where it is found, it is fairly abundant within a few square metres of space. In total, I probably saw in the order of 50 plants. I certainly didn't photograph every plant, but I captured representatives of all populations that I found. The purple vetch appears to be happy to grow nearly anywhere, including up through tall grass, but L. sphaericus generally appears to prefer sites with relatively short surrounding cover such as found along the edge of the loop track, although it is equipped with tendrils and could climb up grass. Most plants were probably not more than 20 cm tall and only had one flower. I found nearly all of them on the uphill side of the loop track not more than a few metres from the track. I did make a couple of transects up to 10 m uphill from the loop track, and a quick reconnaissance to the top of Coronation Hill, but I didn't find any plants there.

I don't know enough about how legume seeds are dispersed. I want to explore the hill to the south of Coronation Hill next, but my gut feeling is that there probably won't be any specimens over there given the current known distribution spans only the northern half of the perimeter of Coronation Hill south of the Summit Road. Given the right conditions, they might be more likely to exist on the northern side of Summit Road.

Posted on November 4, 2019 08:56 AM by crellow