The story of plant evolution is told in the Botanic Garden using five displays. The Evolution of Land Plants Display shows how plants colonised the planet from the sea and charts progress from the Cambrian period until the evolution of flowers in the Triassic period. The Angiosperm Phylogeny Display is laid out as the family tree of flowering plants which are also the focus of The Floral Diversity Displays illustrating the wide variety of ways that plants are pollinated and the methods used to achieve this. The New Zealand Plants Display highlights convergent evolution amongst the flora of this fascinating country, while The Adaptation to the Environment Display shows the strategies plants employ to survive.
The Evolution of Land Plants Display consists of a walk through a sunken dell charting the most important stages in the evolution of plants on land, from the first aquatic green algae, to flowering plants. This ‘evolutionary walk’ takes the form of a journey through geological time from the Cambrian to the Cretaceous using appropriate rocks and fossils to reflect the passage of geological time. Living representatives from the various groups of modern land plants appear along the walk within the geological time zone when they first evolved – mosses, liverworts ferns, and horsetail, in the Devonian, cycads,Ginkgo and other conifers in the Permian and Triassic and flowering plants in the Cretaceous period.
The display is home to some unusual plants like Wollemi Pine, Wollemia nobilis, for many years thought extinct and known only from fossils dating back 200 million years, until a small relict population was discovered in 1994 in Eastern Australia just north of Sydney. It grows alongside the closely related Chilean monkey puzzle, Araucaria araucana with its broad, hard scale-like leaves each armed with a sharp point. Both trees are young plants and have leaves clothing the branches and stems. The display ends with a display of flowering plants that first evolved in the Cretaceous period. The spring flowering Magnolia sprengeri var.diva with huge deep pink flowers and the summer flowering Magnolia sieboldii with nodding white flowers are planted against a backdrop of bay laurel Laurus nobilis and winter’s bark Drymis winteri representing some of the most ancient flowering plant families.
The Flowering Plant Phylogeny Display represents the latest understanding on the evolutionary relationships and classification of flowering plants inferred from comparisons of their DNA sequences. The paths within this collection take the form of a branching tree (phylogeny) of the flowering plants beginning with the most ancient group, the basal angiosperms, from which all the other major lineages of flowering plants have diverged.
The display starts with a raised pool, home to many waterlily species, including Nymphaea odorata. Planted around the pool are other ‘basal angiosperms’, Schisandra chinensis and Kadsura japonica climb up wooden tripods, while underneath Illicium anisatum, a relative of the star anise, grows. A beautiful collection of Magnolias including: Magnolia stellata and Magnolia dolsopa flower in spring. Tender plants are plunged out during summer such as the pepper relative Macropiper nigrum - and the edible cherimoya, Annona cherimola. Some plants in this collection are too tender and must remain in the glasshouse including the most ancient basal angiosperm Amborella trichopoda. From the basal angiosperms two paths radiate out into the display. One is planted with ‘Monocots’ and includes palm, orchid, lily, grass, iris and ginger plant families. The second is planted with ‘Eudicots’ and includes poppy, buttercup, protea, geranium, daisy and pea families. A walk through the display illustrates the rich diversity of flowering plants which can be traced back to a common ancestor group. Interpretation boards give information at key positions in the display.
The Floral Diversity Collections are grown in front of the main house, at the garden entrance and in the glasshouses. Here the display has been designed to highlight the various methods by which flowering plants are pollinated. These ‘pollination syndromes’ have been organised according to the time period at which they were first thought to have evolved. Flowering plants make up 92% of the world’s flora and have many diverse, often specific, relationships with their pollinators. Near to the main gate beetle pollinated magnolias are grown. Adjacent to these the dragon arum Dracunculus vulgaris is one example of fly pollination producing foul smelling flowers in spring as an attractant. A group of plants including Inula hookeri and Echinops ritro represent plants that attract a range of insect pollinators. The woodland orchid Epipactis gigantea is pollinated by wasps while Salvia forsskaolii has the distinctive flower lip and nectar guide lines so familiar in bee pollinated flowers. The pin cushion shaped flowers of Knautia macedonica and the tubular flowers of Lonicera periclymenum attract butterflies and moths. Bright colours of the sun and sugar bird-pollinated bird of paradise flower Strelitzia reginae grow next to the humming bird-pollinated Salvia elegans and Lobelia laxiflora. The goblet-shaped flowers of Cobea scandens and the hardy banana Musa basjo attract bat pollinators. Protea acaulos is pollinated by South African rodents and the Australian Banksia serrata is pollinated by night feeding possums. Underpinning the display is a planting of grasses restios, birch, hazel and willow, representing plants pollinated by the wind. Whilst some of the pollinators do not naturally exist in the UK willow sculptures of what would pollinate them in nature are strategically arranged to link plant with pollinator. The display has been attractively planted and is at its best from spring through to the end of November when specimens from the glasshouse are planted outside to augment the display. An interpretation board and colour fliers obtainable from the welcome lodge make this display popular with visitors.
Forming part of the core Evolution Collection the New Zealand plant display is home to many highly adapted plants including Carpodetus serratus and the aptly named ‘chicken wire’ bush Corokia cotoneaster. Each has fussy or ‘divaricate’ branch patterns and small leaves which are thought to deter herbivores. These similar features on unrelated plants highlight superb examples of ‘convergent evolution’. The lancewood, Pseudopanax crassifloius is represented by both juvenile plants with bronze, toothed edged, hard foliage and adult plants with green, smooth edged foliage. The two distinct stages of growth thought to be an adaptation to avoid young plants being eaten. Sub-alpine and alpine hebe plants are planted in amongst silver-leaved Astelia nevosa and the grass Chinochloa favescens, illustrating some of New Zealand’s mountain habitats. Plants from coastal scrub and evergreen forest communities are grown including Coprosma and Brachyglottis and the flat-leaved celery pine, Phyllocladus trichomanoides. The whole display is dissected by the main garden path giving visitors the opportunity to see many of these extraordinary plants close up.
Plants in the Adaptation to the Environment Display are grown both outdoors and under glass. In the warm temperate zone cacti Echinocactus grusoni and Cleistocactus hyalacanthus from the Americas and the sub-tropical succulents, Euphorbia grandidens and Sarcostemma viminale from South Africa are two examples of convergent evolution’ with stem succulents adapted to a seasonally dry environment.
In the sub-tropical zone orchids, ferns and bromeliads grow as ‘epiphytes’ on the branches of forest trees illustrating some of the rich diversity of plant communities to be found in the canopy of sub-tropical and tropical forests. Carnivorous plants, found worldwide, have evolved strategies to catch and digest insects. In the warm temperate zone the sticky-leaved Drosera capensis and quickly acting venus fly trap, Dionaea muscipula trap insects with sticky leaves and movement. In the sub-tropical and tropical zones the pitcher plants Nepenthes x masteriana and N. truncata produce large liquid-filled pitchers each with glistening sugar deposits as attractants to flies that are enticed into the pitcher only to fall and drown. These and many other carnivorous plants are grown illustrating plants adaptations to trap and digest animals to supplement their nutrient diet when growing on poor soils.Many orchids are displayed, some with swollen psuedobulbs, a useful adaptation to storing food and water enabling some orchids to grow as epiphytes on the branches of trees in the sub-tropics and tropics. These grow alongside bromeliads whose interlocking leathery leaves form ‘vases’ which trap rainwater. The resulting pools attract insect and other animal life whose waste contributes to a nutrient rich pool from which the plant is able to absorb nutrients. Tropical plants like anthurium’s and cycads with hard, evergreen polished leaves, each with a terminal ‘drip tip’, have adapted to the humid wet environments to ensure their leaf surfaces keep dry and avoid a build up of algae and moss.