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7 Mar 2017

Pollination Party for Red Flowers

Red and green flowers win out as the favourite colours of most nectar-eating birds, according to new research conducted by the Royal Botanic Garden Sydney and The University of Sydney.

The research confirmed that many red and green flowers are longer and narrower than other flowers – making them perfect for bird beaks, and not so good for small flying insects.

Australia is home to many red flowering native plants and is known for its associated variety of honeyeaters, parrots and other flower feeders, thriving on nectar as a food source.

The new findings from the Royal Botanic Garden Sydney looked closely at flower shapes, nectar, behaviour and visitation of pollinators and how they vary across closely related plant species.

Flowers are a plant’s fancy way of attracting animals to stop by, pick up some pollen and pass it on to a neighbouring plant where magic happens and seeds are made. Certain flower colours may in some cases attract birds while making flowers less obvious to insects.

Every species of flowering plant has a unique flower type that has evolved in partnership with different means to transport pollen, including insects, birds, and even wind.

Lead author Dr Trevor Wilson is an expert on the Lamiaceae or mint family which includes aromatic exotics such as basil, rosemary and lavender as well as many native Australian species.

Dr Wilson spent many hours studying the inner workings of flowers and was stunned to see how generalised some are to keep the pollinators coming.

“While I focused on the mint family for this research, many of the patterns we observed could be applied to other plant pollinator interactions,” he said.

“Most people have noticed butterflies and bees landing on flowers but there are so many other fascinating pollination stories happening in our gardens that are just too small or happen too infrequently to observe without carrying out careful and dedicated field observations”. 

Our understanding about plant pollinators depends a lot on our assumption that certain flower shapes and colours attract certain pollinators. Although this greatly influences our understanding of plant reproduction, only a limited number of studies have rigorously tested how well this assumption works.

Common examples people might know include the association between birds and red flowers, or moths and white scented flowers.

This research compared flower characteristics with observed pollinator visits (in this case birds, native bees, beetles, flies) to test this assumption across a group of closely related Australian plant species.

An understanding about how pollination strategies have evolved over time could be answered by mapping flower types and pollinator partnerships to our current understanding about the evolution of these plants.

Flower shape as well as 22 flower characteristics were measured for 17 species of Prostanthera, which is known as the Australian mintbush, a member of the mint family (Lamiaceae).

Researchers made pollinator observations in remote areas across NSW and Victoria during the flowering seasons between 2007 and 2009.

Over 343 recorded hours of observation a total of 2496 recorded visits were made of pollinators such as flies, birds, wasps, beetles, native bees and wasps to Prostanthera species.

Despite some surprising exceptions, the shape, colour and features of a flower can indicate what pollinator group is most likely to visit, e.g. bees, birds or beetles and flies. Differences in flower shape tell us that different species of Prostanthera attract a slightly different group of pollinators. The following flower types for Prostanthera were recorded in this study:

  1. Bird flower type: Red or green colour, shape hinders small insects but good shape for bird beaks, lots of nectar
  2. Beetle+fly flower type: flower shapes suits visitors with less specialised mouth parts, lots of access points for insects to access
  3. Bee flower type: Shape suited to landing and access for bee bodies.

DNA techniques were used to demonstrate that the ancestor of Prostanthera was pollinated by bees, and new pollination techniques (e.g. bird pollination) have only recently evolved.

In this study a plant’s flower shape was shown to be a good indicator of which pollinator/s were likely to visit. This study focused on Prostanthera but the patterns could be applied to other plants with similar flower shapes throughout the southern hemisphere.

Pollination is a critical and topical “service” that is essential for food crops and ecosystems around the world. 

Over 75% of the planet’s flowering plants reply on animal pollinators to reproduce and yet many studies indicate significant loss of pollinators around the world.

By better understanding the intricacies of pollination, we are better equipped to protect pollinators and the plants that depend on them.

Many native Australian plants have red flowers to attract birds as pollinators. Nectar and pollen are a major food source for many native birds, the relationship between pollinator and pollinated is win-win.

Birds like wattlebirds, honeyeaters and lorikeets are commonly seen feeding on the red flowers of Grevillea, Bottlebrush and the Waratah, which is both the NSW state flower and state logo. Many people intentionally plant these species to attract birds to their garden.

Great Expectations: Correlations between pollinator assemblages and floral characters in Lamiaceae
  • Trevor C. Wilson (Royal Botanic Garden Sydney)
  • Barry J. Conn (The University of Sydney)
  • Murray J. Henwood (The University of Sydney)
This work was in part supported by two research grants to T.C. Wilson: the Hansjörg Eichler Scientific Research Fund grant (Australian Systematic Botany Society) and the Australian Biological Resources Study (grant RFL212-43)
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