Just under 310,000 higher plant species have been described. However, over 20% of all known plants are currently threatened with extinction. The threats to wild plants are many and varied, including habitat loss, over-exploitation, competition from introduced plants and animals and climate change. Some species will always have been naturally rare.

Botanic Gardens throughout the world are attempting to protect the genetic diversity of wild plants, many of which may yield materials useful to future generations, and all of which are important in the complex interactions of plants, animals, bacteria and fungi that make up living ecosystems. There is not enough space in botanic gardens to house all the rare and threatened species of plants in sufficient numbers; the ideal situation is to first bulk up the number of individuals and then re-introduce them to ‘safe’ natural or semi-natural habitats, where they can evolve and reproduce with relatively little maintenance effort.

Numerous rare and threatened species are grown for conservation at Trinity College Botanic Garden . They include specimens which were collected by Dr. Peter Wyse Jackson, now Director of Missouri Botanical Garden, and Professor John Parnell from the Indian Ocean island of Mauritius, an island where many new species have evolved in isolation from their continental relatives but which have been reduced to alarmingly small populations by the spread of Mauritian sugar cane production.

Mimusops petiolaris

This is a Mauritian forest tree whose numbers in the wild have been radically reduced due to habitat loss. Though the trees that do remain produce many seeds, these will germinate only when the outer layers are removed, a service likely provided by fruit-eating animals or birds. However, because of the loss of habitat, the birds and animals are also likely to have been displaced or become extinct, so any seeds that are produced by the remaining trees will simply fall to the ground and rot.

This is a stark illustration of the high interdependency of animal and plants species and the need to protect all species in whole, functioning ecosystems.

Other rare species were collected by Dr. Stephen Waldren from the remote Pitcairn island group in the Pacific Ocean. The Pitcairn islands have rarely been visited therefore the plants that inhabit them are not well known, even as dried herbarium specimens.

Slipper Orchid (Paphiopedilum insigne)

Paphiopedilum is a genus of orchids native to Asia and Melanesia.  The spectacular flowers with their lower petal transformed into a slipper-shaped trap give this group its common name, ‘Slipper Orchids’.  Orchid flowers have evolved into unusual and often bizarre forms connected to mechanisms for pollination.  Some species are dependent upon a single species of insect for pollination.

Paphiopedilum are much sought after by collectors, and excessive collecting of highly prized species endangers natural populations.  Many are now reproduced by modern micropropagation techniques, where many thousands of plants can be produced from a small amount of tissue cultured in sterile media in a laboratory.

Nolina recurvata

Nolina species come from central American arid zones. Nolina recurvata develops a succulent swollen stem base, which serves as a water storage organ and thereby helps the plant to survive in its arid natural habitat.  The long, curved leaves often get ragged at the tips, these may assist with water uptake from early morning fogs.

Like many central American succulents, Nolina species are highly valued in the multi-million dollar cultivated plant trade.  Many of these species are at risk of extinction in the wild through over-collecting.  All too often there is a lack of basic scientific information about the biology of the species in the wild, which hampers both conservation efforts and the sustainable utilisation of these important resources.

Abutilon pitcairnense

– the rarest plant in the world?

Conservation is a numbers game – the greater the number of individuals of a given species, the greater the genetic variation there is likely to be.  Genetic variation is essential to ensure the future evolution of the taxon, and the ability to evolve may well determine whether the species is able to respond and adapt to effects such as changes in land use and habitat loss, global climate change, the effects of pest and pathogens.

Unfortunately, many species are known from just a single individual.  Abutilon pitcairnense is one example, where just one wild genotype is known from remote Pitcairn Island in the south-central Pacific Ocean.  Pitcairn is famous as the home of the Bounty mutineers, but recent work by Steve Waldren and colleagues from the Botany Department has concentrated on plant conservation issues.  Many oceanic islands contain plants and animals that have evolved in isolation from their continental ancestors, however much of this biodiversity is under threat from land clearance for tourism and agriculture, and from threats posed by invasive non-native species.

Working closely with the islanders, the Trinity Botany team have vegetatively propagated Abutilon pitcairnense, and now have replicates of the same genotype both on Pitcairn and at Trinity Botanic Garden.  The next step in the recovery of this species will be to assess genetic variation in seed progeny using molecular markers, and to develop a breeding programme to maximize genetic variation in subsequent generations.