Appendix 4

Russula vivida

What do the numbers mean?

A case study based on the Rhytismataceae

The 2,500 species in Herbarium PDD represented by 3 or fewer collections include exotic species found in New Zealand only on introduced plants, as well as common species which have not been searched for intensively. The relatively well-studied Rhytismataceae provide the opportunity to ‘test’ how many taxa in this list may truly be rare.

The Rhytismataceae are a group of discomycetes which have been intensively studied in New Zealand native forests over the past 15 years. There are about 67 species known for New Zealand, represented in PDD by over 1100 collections.

8 of these 67 species are known only from introduced plants, or are doubtfully identified. They have been excluded from the data.
Some species are far more commonly collected than others (Fig. 1).
15 species are known from 3 collections or less (Fig. 2). Why have these species been so rarely collected?
- Lophodermium alpinum is a spring-fruiting, alpine species, and is probably common, but not often collected.
- Lophodermium rubrum has been found only on the Poor Knights Islands (on Cortaderia splendens) – it is possibly restricted to the Poor Knights, or may occur more widely on Cortaderia splendens.
- Colpoma agathidis has recently been found to be more common in the very south of New Zealand than the north – the lack of collections may represent a geographic bias to collecting effort.
- Colpoma nothofagi, on the other hand, has been searched for extensively, but been found only twice.
- Propolis dendrobii was found on fallen leaves of Dendrobium sp. It has been looked-for often, but found only once – maybe this is a truly rare species.
- etc.
In summary, maybe 4 or 5 of the species of New Zealand Rhytismataceae represented in PDD by less than 3 collections are truly rare. The same may also be the case for other similarly-sized families of fungi.