Monday, August 13, 2012

PG Plant: Africa’s Biggest Flower

One big family: many big flowers
In the world of flowering plants morphological characters such as shape, size, colour, and odour and display pattern are both astonishing and interesting evolutionary phenomena. When size and shape of flower is the main consideration, the family  Aristolochiaceae is something to be reckoned with. African Aristolochiaceae belong to two monophyletic groups: Aristolochia and Pararistolochia. Aristolochia is a genus of evergreen and deciduous woody vines and herbaceous perennials. The simple leaves are alternate and cordate, membranous, growing on leaf stalks with no stipules. Pararistolochia, on the other hand, is characterised by trimerous flowers, which are much curved, and a reproductive structure that is subdivided into up to 24 lobes. The fruits are berries in contrast to all other members of Aristolochiaceae that have capsules. In Nigeria and many parts of Africa, Aristolochiaceae is well represented and a good example is Aristolochia ringens which is not indigenous but is naturalized at IITA-Ibadan. While Pararistolochia tenuicauda is endemic to Oban Division of Cross River National Park, Cross River State, Pararistolochia goldieana is found widely in Nigeria.

Pararistolochia goldieana: the African equivalent of Rafflesia
Pararistolochia goldieana, commonly known as the PG plant, is found in lowland evergreen forest, often in disturbed areas. This climber almost certainly has the largest flowers (40cm in diameter x 50cm in length) of any African species of flowering plant. It is the African equivalent of the South East Asian Rafflesia arnoldii (the world’s largest flower), matching it in habitat, colour and scent.

PG plant possibly fly-pollinated
No formal pollination studies on the PG plant have been reported but it is known that most species of this genus have a specialized pollination mechanism. The plants are aromatic with a fetid strong scent and purple-brown colour that attract small flies. The inner part of the perianth tube is covered with hair, acting as a fly-trap. These hairs then wither to release the fly, covered with pollen.

Pararistolochia: food plants for larvae
The leaves of many species of Aristolochiaceae are eaten by pipe-vine swallowtail butterflies. The PG plant contains a chemical compound known as aristolochic acid. This is sequestered by caterpillars of some butterflies in their bodies, making them unpalatable to birds.  Similarly, an Australian relative of the PG plant, Pararistolochia praevenosa, is the main food plant of caterpillars of the Richmond birdwing butterfly, Ornithoptera richmondia, and this ecological relationships with insect larvae will be an interesting study of research.

The World of the PG plant
Though the PG plant is the largest flower in Africa and of great interest for this reason alone, it has been classified as threatened due to habitat loss. Surprisingly, little is known about remaining numbers and distribution but in Nigeria a certain place to find a thriving population is in the IITA forest. Now you have another good reason to support the work of the Forest Project and visit IITA-Ibadan – which is a hotspot for biodiversity in Nigeria.
Olabode A. Emmanuel:

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