Published online by Cambridge University Press: 05 June 2016
The study of a range of plants in the wild or on display in a Botanic Garden reveals a bewildering array of floral types. Many books describe in some detail a selection of pollination mechanisms, often discussing in highly technical botanical language the variety of floral structure. Special terms have, quite properly, been devised by botanists to enable them to write concise, accurate plant descriptions. Although the botanical literature reports extensively on the structures involved in reproduction, in our opinion, it does not pay sufficient attention to the variety of breeding systems in plants, systems of which complex structures and pollination mechanisms are only a part.
We have noted in earlier chapters the role of the internal sources of genetic variation, namely mutation and recombination, and have seen that a vast number of gametic types is theoretically possible as a consequence of these factors. Which gametes are actually brought together to form the zygotes, however, depends, to a great extent, upon the breeding system of the plant concerned.
In this chapter, as a prelude to our discussions of variation within and between species, we consider three areas:
A. The different breeding systems found in flowering plants.
B. Breeding behaviour discovered in studies of wild populations.
C. The evolution of breeding systems.
Our account discusses how studies of breeding behaviour have developed, and emphasises that a knowledge of the different breeding systems provides an indispensable framework for understanding the complexities of patterns and processes found in nature.
A. The different breeding systems found in flowering plants
There are three basic breeding mechanisms, which we examine in turn.
Outbreeding
In many animal groups outbreeding – crossing between different individuals – is rendered likely by sexual differentiation. In higher plants, however, separation of the sexes is the exception. According to Richards (1979), only about 4% of the flowering plants are dioecious. A slightly higher figure is reported by Renner & Ricklefs (1995), who note that c.6% of angiosperm species are dioecious, these species being distributed amongst 7% of genera. The incidence of dioecy varies in different floras. While only c.3% of British flowering plants are dioecious, much larger percentages are reported, for example, from groups of distant oceanic islands such as Hawaii (28%) and New Zealand (13%).
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.