Part of my role as Collection Manager at Te Papa herbarium is contributing to the further development of our dried plant collection. At the herbarium we are interested in collecting indigenous and naturalised New Zealand plant species for future scientific investigation and as an historical record.
One of our recent collection development projects focused on collecting as many species as possible in a specific coastal plant community, Hue te Taka in Wellington. One of the species growing here is the naturalised succulent, Cotyledon orbiculata. This species is a relatively common coastal plant, at certain localities, along the east coast of New Zealand.
To preserve their specific characteristics properly, succulents take a bit more thought and time to prepare as a herbarium specimen than typical flowering plant specimens. However, this is probably one of the easiest succulent species to prepare. While still fresh, I was able to longitudinally section the flower stem and scoop out the flesh. I then cut the leaves in half and, using a razor blade, skinned them so very little flesh remained. The specimen was then dried out completely in our cabinet drier.
Other internet resources talk about preparing specimens in this way. Cross-sectioning some species (of cacti, for example) may provide further detail or identification characteristics and using alcohol or boiling water to kill the cells, before pressing, enable it to dry completely and prevent it from growing in storage.
Older specimens of Cotyledon orbiculata at Te Papa have been dried conventionally, without any special preparation, with varying success. I think the leaves in particular can be preserved in a truer form if prepared in this ‘skinned’ way. I doubt that this species would be able to grow in storage.
The end result was a good herbarium specimen that was able to be easily mounted. Things to improve on: a few nicks can be seen in the leaves from getting too close to the leaf surface when skinning and the placement of lower right leaf should be lifted above the label. Spreading out one of the flowers enables a clear display of the flower parts. Similarly, flowers may be cut in half and the two halves pressed.
I’m relatively new to preparing succulents as specimens. I’m interested in finding the method which results in specimens true to form with as much scientific value (e.g. intact DNA tissue) as possible. A South Australian colleague, expert in this area, will publish his treatment of Australian fereal opuntioids later in the year. I’ll be sure to reference it, so watch this space.
Thanks Matt. I’ll try freezing next time. Good point regarding DNA. The method I described was also labour intensive, but fun.
Ok, in South Africa, home to many Crassulaceae and Aizoaceae, I froze to burst cells and there kill plants and making the water more “releasable”. I then dried as per standard procedure, just replacing blotting (news) paper on a daily basis to begin with. Rather labour intensive, but no nicking of leaves, etc. Also so-doing, you have more tissue on the sheet to potentially sample for DNA analyses.