Dioon edule - a cycad

Although they resemble palms, cycads are a much more primitive group of plants which are in fact more closely related to conifers.  Dioon might be described as a living fossil- the few remaining cycads in the world are the remnants of a group which diversified and dominated vegetation types in the Triassic period.  Cycads have been extensively collected for their attractive form, but because they are inherently slow growing, many are now on the verge of extinction due to over-exploitation.  Mexican rural communities collect the large seeds of Dioon edule as a source of food; the plant therefore provides an important local resource, which is in need of conservation.

Cycads have separate male and female plants.  The ripe male cone of Dioon is kept at about 10° C above ambient temperature by the plant’s own metabolic processes that generate heat, and which is probably linked with the pollination mechanism.

Understanding the evolutionary relationships of plants, their varied physiological processes which allow them to exploit different ecological niches, and how their different communities have varied over time in response to global changes in the biological, soil and climatic environments all contribute to our understanding of plant biodiversity.  This understanding provides the means of conserving plant resources for the benefit of future generations.  These areas of plant biology are all central to botanical teaching and research in Trinity College.

Strelitzia reginae

The spectacular flowers of S. reginae suggest its common name – ‘Bird of Paradise Flower’ – though it is more usually called ‘Crane Flower’ in South Africa.  The plant has another close association with birds: it is usually pollinated by sunbirds.  The bright orange sepals are the main attractants, along with nectar produced by modified blue petals.  When a bird lands on the horizontal ‘perch’ the anthers are revealed from beneath the blue petals, dusting the bird’s belly with pollen.  The blue petals also hide the stigma, which is receptive before pollen is released (protogyny) favouring outcrossing.  The inflorescence produces a succession of flowers, each lasting about one week.

Strelitzia reginae is a native of the Eastern Cape and Kwazulu-Natal in South Africa, growing in moist soils along river banks.  It is widely grown commercially, and one cultivar was named in honour of Nelson Mandela.

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.

Peperomia hombronii growing in the cloud forest of Tahiti

Peperomia species have minute flowers aggregated together onto a narrow spike.  As flower characteristics are the main means by which we distinguish different species of higher plants, the small flowers make identification of Peperomia species difficult.  Over 1000 Peperomia species occur worldwide.

Research in the Botany Department is investigating speciation and evolution in Pacific Island Peperomia species by extracting DNA and analysing genomic sequences.  The species on display in the Cycad House were all collected during departmental expeditions to the south Pacific, and many of them are  likely to be in cultivation solely at Trinity College Botanic Garden. The species in the Trinity collection include samples from Pitcairn Island and also the Marquesas Islands that may be new to science.

Kalanchoe tomentosa

Kalanchoe tomentosa a succulent plant with densely hairy leaves.  Both the succulence and the hairs help the plant to restrict water loss.

Cycas revoluta

Cycas revoluta, a large cycad here showing the dense cluster of reproductive megasporophylls in the centre.

A female Cycas revoluta

A female Cycas revoluta showing the reproductive megasporophylls in the centre of the leaf rosette and the large ovules