Recurating the Apocynaceae carpological collection

What is a carpological collection?

The carpological collection housed within the Herbarium at Kew contains the plant material too chunky to be mounted onto herbarium sheets. After the reorganisation of the herbarium collections (to follow the Angiosperm Phylogeny Group (APG III) classification) in 2010–2015, it became clear that the Apocynaceae carpological collection needed some curatorial care.

One size does not fit all

Unsurprisingly, not all plant material can be pressed flat and dried to fit onto a herbarium sheet. When new plant material arrives at Kew, the specimens are identified and named. Any bulky material (usually larger than 3 cm in depth) is separated and placed into an appropriate sized archival box.

The carpological material (usually fruits and seeds) is cross-referenced with the original herbarium specimen (and any other ancillary collection where appropriate). Once labelled, it is housed mostly in drawers, following the same family and geographical sequence as the herbarium specimens in the cupboards. This cross-reference notifies researchers using either collection that additional material is available. 

Not all plant families have carpological collections, only those with species which produce bulky fruits or seeds, for example, the Leguminosae, Rubiaceae and Apocynaceae.

The Apocynaceae family

Apocynaceae are one of the ten most diverse families of flowering plants, with around 5,500 species in 378 genera. Some are timber trees, others are important medicinally, and many have horticultural merit.

Apocynaceae are found all over the world but are most diverse in tropical regions. In wet forest, they are mostly trees and shrubs; in seasonally dry environments mostly herbs or slender vines, but there are also several genera of cactus-like stem succulents.

Closely related to the coffee family, Apocynaceae have tubular flowers which, in the more specialised members of the family (formerly regarded as a separate family: the Asclepiadaceae), are almost orchid-like in complexity – the floral structures have co-evolved with their (mostly) insect pollinators for ever more precise control of pollen transfer.

Although most Apocynaceae seeds are wind-dispersed, with a parachute of hairs and a dry seed (for example Wrightia), seeds in other genera are embedded in mango-like flesh which is attractive to monkeys (Saba). One Apocynaceae even forms mistletoe-like fruit that are eaten and dispersed by birds (Vallesia).

Checking for accepted names

Using a generic sequence compiled by Kew's Apocynaceae specialist Dr David Goyder, the volunteers were able to check whether a generic name was accepted or a synonym. By searching for the corresponding herbarium sheet, they were able to check that both were updated accordingly. Matching collector name, date, locality and any other information provided with the plant material meant the volunteers were able to confidently match specimens. Here Pat explains the process:

“Sometimes we could not find the corresponding herbarium sheet matching the carpological label. In these cases, we looked under all the species for a genus to see if the specimen had been renamed.  Sometimes the shape of the fruit or seed gave us a clue where to look.  Occasionally the situation was more complicated where one genus was subsumed into another. One example of this was in genus Marsdenia, where some specimens were filed under Gymnema, and some specimens from India were filed under genus Wattakaka. Once we had established the accepted genus and species, where available, the particular carpological specimen was re-labelled with the updated information. Where the information was missing or uncertain the specimen label was written in pencil.”

Having spent so much time with the collection, Pat and Kay have become extremely familiar with the family and are now able to identify material, at least some to genera, by the fruit shapes and characteristics, which has helped them enormously as they've proceeded with the project. The task was completed in April 2017 and although there are a small number of specimens needing specialist investigation, the collection is now in excellent working condition, which we hope will instigate further research and use of this family.

In total the volunteers worked through 39 drawers, replacing approximately 10% of the boxes. The total number of carpological specimens add up to just over 1,000, representing 77 genera, and we welcome researchers to use this now accessible resource. Special thanks to Pat Keep, Kay Sharp and Beth Schmidt for their immense amount of help, support and enthusiasm in seeing this project through to completion.

The future of the carpological collection?

In an ideal world, and to avoid ancillary specimens losing corresponding parts in the future, the carpological collection could be imaged and databased, especially the type material. However, there are issues with imaging three-dimensional plant material at a reasonable cost. Technology is developing all the time, and exciting images have already been made using techniques such as those created by CT scans. 

Finally, the unique fruits hold aesthetic value and would lend themselves well to being on exhibition, which in turn would raise awareness of this unique and significant collection.