ARTICLE : Diplodium alveatum at Stokes Valley –
a new North Island record

 Diplodium alveatum at Stokes Valley – a new North Island record.

Diplodium alveatum at Stokes Valley.   Photo: Jeremy Rolfe.

In February 2006, I found a single flowering specimen of an unusual greenhood under manuka on a bank on my property at Stokes Valley – about 3 metres from the back door of my house.   The flowering stem was approximately 150 mm tall.   I photographed the plant and sent images to Ian St George and Peter de Lange, who both quickly identified it as Diplodium (Pterostylis) alveatum.

D. alobulum occurs a couple of metres away, and D. trullifolium is also found in Stokes Valley, but those species are both winter flowering.

D. alveatum is an Australian greenhood orchid related to the New Zealand endemics, D. alobulum, D. brumalum and D. trullifolium.   It was first discovered in New Zealand in May 1998, growing under manuka and gorse in northwest Nelson.   Several hundred plants are known from the area, and the species is classified “Coloniser” in the Department of Conservation’s New Zealand Threat Classification System.

Many Australian orchids have arrived in New Zealand from seed blown across the Tasman Sea on the prevailing west to east winds.   Of those that have established here, many remain scarce because the New Zealand environment does not provide the conditions they need to flourish: for example, suitable insect pollinators may be lacking.

It seems as if D. alveatum is becoming established in northwest Nelson, but it is too early to say whether the plant at Stokes Valley represents an extension of the range from Nelson; it may simply be a chance germination of seed blown from either Nelson or Australia.

Photos of D. alveatum can be seen on the NZ Plant Conservation Network website, www.nzpcn.org.nz (search for vascular plant > Diplodium alveatum).   If you find D. alveatum growing in the lower North Island, please report your find to John Sawyer at the Department of Conservation, jsawyer (at) doc.govt.nz.

The occurrence of the species at Stokes Valley reminds us all to keep an eye out for the unusual wherever we happen to be.

Jeremy Rolfe