Name that Flower: The Identification of Flowering Plants: 3rd Edition

By Ian Clarke and Helen Lee

Name That Flower is a valued source of clear and concise information on identifying flowering plants from around the world, both cultivated and in the wild.

This edition is updated to align with current systems of plant classification that incorporate advances in molecular DNA analysis. It includes more than 130 detailed line drawings, 64 colour pages and information on 46 plant families. The illustrations depict a selection of widely distributed gardens plants and weeds, and species native in eastern and southeastern Australia. Easily navigated, the book facilitates the successful use of standard identification manuals and online resources available in most parts of the world and introduces the reader to the arrangement of flowers on plants, reproduction, plant structure and function, and the way species are grouped and named. Methods for dissecting flowers and observing their structure for identification purposes are clearly described.

This bestseller is used extensively as a teaching text in numerous courses concerned with the natural world, such as agriculture, horticulture, botany, environmental management and landscape design, as well as botanical art. It is an essential reference for serious gardeners and keen botanists, professional and amateur.

• Language: English
• Publisher: Melbourne University Publishing Ltd
• Release date: Nov 19, 2019
• ISBN: 9780522876055

Ian Clarke

Ian Clarke is an author, the founder of the Kiwoko Mission Hospital, and the mayor of the Makindye Division of Kampala. He has spent over twenty-five years in Uganda and has witnessed the country's development over the last quarter of a century.

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After working in a variety of technical jobs, including with the Forests Commission of Victoria and the Botany Department of The University of Melbourne, Ian Clarke was for many years employed in the plant identification service of the National Herbarium of Victoria. He transferred to a position as honorary associate there in 2003. He is the author and illustrator of a companion text, Name those Grasses: Identifying Grasses, Sedges and Rushes, published by the Royal Botanic Gardens Victoria in 2015. Between 1975 and 1990 he was associated with the Council of Adult Education in Melbourne as a tutor in flowering plant identification.

Helen Lee holds a Master of Science degree from the University of Melbourne. After lecturing in botany for two years at Queen’s University, Belfast, she was for many years a part-time tutor in the botany departments of Melbourne and LaTrobe Universities, and a tutor with the Melbourne Council of Adult Education. Upon retirement, she took up a position as Honorary Research Fellow in the Botany Department, LaTrobe University. Her research interests included the morphological characteristics of plants that resprout after fire, and arid zone ecology. She has been a member of the Royal Society of Victoria and the Australian Systematic Botany Society.

Praise for earlier editions of Name That Flower

For anyone interested in identifying Flowering Plants and understanding more about their structure, this book is the best of its kind.

Australian Natural History

Equips the reader with the techniques and interpretative skills needed to make intelligent use of floristic works covering not just the Australian flora but other regions of the world, and in doing this so clearly and concisely it must be thoroughly recommended. Kew Bulletin, UK

NAME

THAT

FLOWER

IAN CLARKE & HELEN LEE

MELBOURNE UNIVERSITY PRESS

An imprint of Melbourne University Publishing Limited

Level 1, 715 Swanston Street, Carlton, Victoria 3053, Australia

[e-mail]

www.mup.com.au

First published 1987

Reprinted 1989, 1990, 1992, 1993, 1994 (twice), 1995, 1997, 1998, 2001

Second edition 2003

Reprinted 2006, 2009, 2011

Third edition 2019

Text © Ian Clarke and Helen Lee 2019

Illustrations and photography © Ian Clarke, 2019

Design and typography © Melbourne University Publishing Limited, 2019

This book is copyright. Apart from any use permitted under the Copyright Act 1968 and subsequent amendments, no part may be reproduced, stored in a retrieval system or transmitted by any means or process whatsoever without the prior written permission of the publishers.

Every attempt has been made to locate the copyright holders for material quoted in this book. Any person or organisation that may have been overlooked or misattributed may contact the publisher.

Cover design by Nada Backovic

Cover images by Ian Clarke

Typeset by Megan Ellis

Printed in Australia by McPherson’s Printing Group

Cover images

Front, clockwise from top left:

Backhousia myrtifolia   Family 27 MYRTACEAE

Myoporum petiolatum   Family 40 SCROPHULARIACEAE (see Plate 31f)

Elaeocarpus reticulatus  Family 23 ELAEOCARPACEAE

Lophostemon confertus   Family MYRTACEAE (see Plate 20a–d)

Back, clockwise from top left:

Elaeocarpus reticulatus Family 23 ELAEOCARPACEAE

Pomaderris aspera Family 19 RHAMNACEAE

9780522876048 (paperback)

9780522876055 (ebook)

This book has been produced with the support of Royal Botanic Gardens Victoria

Contents

Acknowledgements

Introduction

1  Getting Started

Background

Some essential information

Using this book

Notes on the illustrations

2  The Structure of Flowers

Structure of a basic flower

Variation in floral structure

3  Inflorescences—the arrangement of flowers on the plant

Solitary flowers

Multi-flowered inflorescences

Racemose branching

Cymose branching

Common practice in applying inflorescence terminology

4  Reproduction

Pollination

Fertilisation

Development of the seed

Development of the fruit

Germination

5  Introduction to Plant Structure and Function

Cells

Stems

Leaves

Roots

The vascular system

Plant growth

List of plates 1–17

6  Classification and Nomenclature—grouping and naming

Classification

Nomenclature

7  The Process of Identification

Equipment

Choosing the flower to look at

Interpreting what you see

Cutting a section

Using keys

Points to note

Computers and keys

Sample bracketed key to species illustrated in this book

8  Plant Families

Magnoliids

  1  MAGNOLIACEAE Magnolias and Tulip Trees

  2  LAURACEAE Laurels and allies

Monocotyledons (Monocots)

  3  ARACEAE Arum Lilies, Duckweeds and allies

  4  COLCHICACEAE Autumn Crocus, Early Nancy, Milk Maids and allies

  5  LILIACEAE Lilies

  6  ORCHIDACEAE Orchids

  7  IRIDACEAE Irises and allies

  8  ASPHODELACEAE Asphodels, Flaxlilies and Grass-trees

  9  AMARYLLIDACEAE Belladonna Lily, Garlics, Onions and allies

10  ASPARAGACEAE Asparagus and allies

11  POACEAE Grasses

Eudicotyledons (Eudicots)

12  PAPAVERACEAE Poppies and Fumitories

13  RANUNCULACEAE Buttercups and allies

14  PROTEACEAE Proteas, Banksias, Grevilleas and allies

15  DILLENIACEAE Guineaflowers

List of plates 18–34

16  CRASSULACEAE Stonecrops and Orpines

17  LEGUMINOSAE Legumes

18  ROSACEAE Roses and allies

19  RHAMNACEAE Buckthorns

20  MORACEAE Mulberries and Figs

21  CASUARINACEAE She-oaks

22  CELASTRACEAE Bittersweet and Spindle-tree Family

23  ELAEOCARPACEAE Oliveberries, Aristotelias and Pinkbells

24  HYPERICACEAE St John’s Wort and allies

25  EUPHORBIACEAE Spurges

26  ONAGRACEAE Evening Primroses, Fuchsias and Willowherbs

27  MYRTACEAE Myrtles, Eucalypts, Bottlebrushes and Tea-trees

28  RUTACEAE Rue, Citrus, Boronias and Correas

29  MALVACEAE Mallows, Baobabs, Lindens and Bottle Trees

30  THYMELAEACEAE Daphnes and Riceflowers

31  BRASSICACEAE Cabbages, Mustards and Wallflowers

32  LORANTHACEAE Mistletoes

33  DROSERACEAE Sundews

34  CARYOPHYLLACEAE Campions, Catchflies, Chickweeds and Pinks

35  CHENOPODIACEAE Saltbushes and Samphires

36  AMARANTHACEAE Amaranths

37  ERICACEAE Heaths and Heathers

38  BORAGINACEAE Borages and Forget-me-nots

39  SOLANACEAE Nightshades and Kangaroo Apples

40  SCROPHULARIACEAE Figworts, Myoporums and Emubushes

41  LAMIACEAE Mints and Mintbushes

42  STYLIDIACEAE Trigger plants and Styleworts

43  GOODENIACEAE Fanflowers and Goodenias

44  ASTERACEAE Daisies

45  PITTOSPORACEAE Pittosporums

46  APIACEAE Celery, Carrot, Parsley and allies

References and Websites

Symbols, Abbreviations and Contractions

Glossary

Index

Acknowledgements

Grateful thanks are again extended to those who assisted with the preparation of the first two editions of this book.

We are most gratified by the continued acceptance over several decades now of this text by lecturers and students in many plant-related fields, as well as naturalists and botanical artists both amateur and professional. Without their interest and response to the book the motivation for a third edition may well not have arisen.

Help has been received in many ways with the compilation of this third edition. We are grateful for assistance with the intricacies of computers, with location of plants in the field for photography, with tracing botanical literature, and for providing comments on drafts of the manuscript.

Many thanks to Philip Bertling, Dr Joanna Birch, Prof. David Cantrill, Geoff Carr, Anthony and Rob Cross, Darcy Duggan, Leanne Hanrahan, Dr Meg Hirst, Dr Teresa Lebel, Dr Dan Murphy, Dr Sue Murphy, Dr Roger Spencer, Val Stajsic, Sally Stewart, Dr Frank Udovicic, Neville Walsh.

Mr A.W. Beudel provided the photographs used in Plate 9f and i, Assoc. Prof. Dr B.T.O. Lee the photograph in Plate 27a, and Mr T. Phillips the photograph used in Plate 28h. Mr C. O’Brien assisted with photography for Plates 8a and b.

This third edition was prepared during Ian Clarke’s tenure as Honorary Associate at the National Herbarium of Victoria, Royal Botanic Gardens Victoria. Completion of this project has been much aided through access to the excellent botanical collections, library and facilities of the Herbarium, and the generous support of Herbarium and Gardens staff. We thank Professor Tim Entwistle (Director and Chief Executive) and Professor David Cantrill (Executive Director Science) for their support.

Introduction

For the amateur, whether gardener, bushwalker or naturalist, and even for the professional scientist who works in other fields of biology, there has been no readily available source of information on how to go about identifying Flowering Plants. There are many books of excellent photographs but if the plant of interest is not included, what do you do next? With the advent of computers and the internet, countless plant photographs can be revealed with the click of a mouse. But can you be sure of their identity? Botanical science has certainly not been immune to the technological revolution affecting so many facets of life in the 21st century.

More and more plant identification resources are becoming available online, but at present however, practical Flowering Plant identification still relies on the skills of dissection, observation and interpretation, aided by the accumulation of experience and knowledge. These attributes are not readily incorporated into electronic devices. We have attempted here to record the traditional approach to plant identification while pointing to some of the innovations, such as multiple access keys, that are part of the electronic age.

This introduction to the subject describes the structure of flowers and the process of identification, with the intention of making the procedure more straightforward and more conclusive. It is intended to be used in conjunction with other published work such as field guides and floras (a flora is a book about the plants of an area, usually with descriptions and keys for identification; some are now available online). The botanical language is often seen as a stumbling block and although many terms have been explained within the text, the glossary included here (now much extended) covers most of the terminology used in current floras. The glossary should also help readers who wish to delve further into the botanical literature provided in the references.

The principles of plant identification are universal so the basic information presented here is applicable anywhere in the world. Many of the drawings and photographs depict very widespread species, sometimes established well beyond their original ranges. The samples for illustration were all sourced from plants growing wild or in gardens in southeastern Australia.

The botanical names used here for plant species generally follow those accepted in the new online versions of

Flora of Victoria (https://vicflora.rbg.vic.gov.au) and

Horticultural Flora of SE Australia (https://hortflora.rbg.vic.gov.au).

Numerous changes have been implemented in this third, revised edition. Most of the obvious text changes are in response to the significant progress made in recent decades in our understanding of plant relationships through advances in DNA analysis. These advances have underpinned proposals to modify older plant classification schemes considerably, and precipitated the publication of a new, more collaborative approach which has been well received by the botanical community. The new classification scheme (discussed further in Chapter 6) has necessitated rearranging the sequence of plant families in this edition. (In Chapter 8, families are numbered to assist with their location in the text; the numbers have no relevance beyond this book.) Accounts of several extra families have been added, and changes to the limits of others have meant that some families are now much smaller than they were, and some are much larger. In all, the selected families serve to illustrate a broad range of structure while still keeping the book to a manageable size.

Digital photography and computer software have allowed the range of photographs to be improved and extended, particularly close-ups taken with the aid of a microscope.

The ‘routes through keys’ sections in previous editions have been omitted since the texts upon which they were based are now long out of date. A key to the species illustrated in this book has been included to serve as an example of the way keys are constructed, as well as to help establish if an unknown plant sample can be matched with an illustration.

Background

The earliest evidence for land plants comes from the Ordovician period around 460 million years ago (460 Ma) where spores produced by plants resembling present day mosses and liverworts have been found. The evolution of stronger stems, water transporting tissues, and seeds, enabled plants to diversify and exploit new niches. By the Carboniferous period (358–298 Ma) tropical forests, dominated by tree-like species and primitive seed-bearing plants, formed vast ‘coal-forming’ forests in the northern hemisphere. Ancestors of plants that we are familiar with today such as conifers (pines, firs, spruces, monkey puzzles) appeared later in the Carboniferous period (315 Ma). The significant coal deposits of South Africa, eastern Australia, India and South America are much younger, formed from deciduous forests that covered temperate southern regions as far south as 80 degrees latitude. The most spectacular change to global vegetation occurred in the Cretaceous period when flowering plants rose to ecological dominance (100 Ma) replacing a vegetation dominated by conifers, ferns and groups of seed plants now extinct. Today just five lineages of seed plants survive, the most diverse group being the Flowering Plants with about 300 000 species. The long geological history and diversity of land plants contrasts markedly with that of the genus Homo, to which we belong. Evidence of early humans appears just 2.1 million years ago, and modern humans (Homo sapiens) have been here for only 300 000 years.

The term botany is derived from a Greek word meaning ‘plant’ and is the branch of science that investigates plants. However, plants were important to the economy of humankind long before any scientific studies took place. People had to know which were good to eat, which were harmful, had medicinal value or could be used for making shelters, baskets and clothing. Some of the earliest non-religious books were the herbals which contained descriptions of plants with their medicinal properties and recipes for herbal remedies. Plants containing hallucinogenic compounds are part of the folklore in many lands, having a particular place in religious ceremonies. One important ingredient of the witches’ brews of mediaeval Europe was Deadly Nightshade, a relative of the potato and tomato. The use of Cannabis is well-documented; in Egypt, for example, it has been in use for over 4000 years.

Systematics and taxonomy are two interlinked branches of modern botany, and deal with plant form, how plants resemble each other or how they differ, how they can be assembled into groups that reflect their evolutionary history, and how these different forms and groups can be uniquely described and named. But why are names so important? It is certainly easier to talk about a plant, or buy one for the garden, if you know what it is called. All plants have a scientific name that applies to one sort of plant only and has international recognition. These names are the keys to the wealth of information about plants available in the scientific literature and increasingly via the internet. Many amateur naturalists shy away from using them but they are useful in recognising relationships as well as being necessary for accurate identification, which is an essential prerequisite to any discipline that involves plants.

Some essential information

In order to identify any Flowering Plant, in a scientific and conclusive way, one needs to understand:

•the structure of the flower, and of the vegetative parts

•the botanical terms used in descriptions

•how to use reference books, and in particular, botanical keys

•something about plant relationships (the classification system).

These topics are discussed more fully in Chapters 2 to 7; the following paragraphs introduce a few terms and concepts that form necessary background.

The system of naming plants now in use was established in 1753 by a Swedish naturalist Carolus Linnaeus. When Linnaeus put forward his scheme in the book Species Plantarum, all organisms were classified into one of two kingdoms: plants or animals. The criteria for their separation were that plants were immobile and neither ate nor breathed, whereas animals moved, breathed and ate. As new organisms were discovered they were assigned to one of these two kingdoms, but by the early twentieth century it had become obvious that this traditional division could not be sustained. For introductory purposes here, a simplified division of the plant kingdom can be made into Algae (including seaweeds and freshwater forms), Mosses and other moss-like plants, Ferns and their allies, Conifers (pines, cypresses, firs and their relations) and Flowering Plants. The Fungi, including moulds, mushrooms and toadstools, are no longer considered part of the plant kingdom.

Many flowers are large, brightly coloured and scented, while others may be quite inconspicuous, but the plants that bear them all make up the group ‘Flowering Plants’. Technical names proposed for this group include Angiospermae, Magnoliophyta, and Anthophyta. Traditionally, two major subgroups of Flowering Plants have been recognised, commonly known as the Dicotyledons and Monocotyledons. (These names are often contracted to Dicots and Monocots and that usage will be adopted in this book.) Continuing research over the last several decades, particularly using the advances in techniques for extracting and comparing plant DNA samples, has necessitated a reassessment of these traditional major groups.

The main subgroups of Flowering Plants are further divided into orders, families, genera (singular—genus) and species. A species is a kind of plant, possessing a unique set of characteristics; similar species are grouped into genera. A species has a two-word Latin name, e.g. Acacia pycnantha; the first word is the name of the genus (Acacia) and the second is the specific epithet (pycnantha). The common name of this plant is Golden Wattle. Classification and nomenclature are dealt with more fully in Chapter 6.

In contrast to scientific names, common names are not subject to any rules or guidelines of construction or use. Many plants have one or more common names in the language of the region where they grow, but conversely many plants have no common name at all. Further, common names are not universal (the same name may be used for different plants in different regions), so their use may lead to errors and confusion. The use of scientific names is recommended as they eliminate many mistakes in identity and are international in application.

In previous editions of this book common names have been written with lowercase initial letters. This convention however can make the limits of the name unclear, for example which of the words ‘common red-flowered yellow gum’ are simply qualifying adjectives and which should be read as part of the name? In this edition we have changed to uppercase initial letters for common names where these refer to particular species or groups. In more general contexts, lowercase may be used. As well, we have avoided hyphens within common names unless the inclusion of a hyphen significantly enhances clarity or readability.

Much of this book is taken up with description and illustration of flowers. Why is there such emphasis on floral structure? Linnaeus based his system of classification on the characteristics of the sexual reproductive organs and these are found in the flower. Even today floral structure still plays a significant role in plant classification, despite much additional information being available, for example, about anatomical, chemical, and genetic characteristics. An understanding of the way flowers are constructed is a major key to identification because flowers are usually readily accessible, and the relative positions of the various floral parts (the floral structure) remains reliably constant, even if a species grows in a range of habitats which may result in considerable variation in the general appearance of the whole plant. Compared to, say, features of stems and leaves, the number, appearance and relative position of the floral parts are more readily described in a way that can distinguish one species from another. In addition, for people who wish to get to know plants, whether for professional or interest reasons, flowers are generally more memorable, and the details of their structure can assist with establishing a mental register of species and groups.

An appreciation of the way flowers are constructed, and familiarity with the descriptive language, will help the reader to see that plants are not isolated organisms, but form natural groups that are related to each other. Some groups are easy to spot: the orchids, wattles, gum trees and bottlebrushes, for example. However, the close relationships of genera in a family are not always immediately obvious, for example, the grouping of gum trees and tea-trees, or of proteas and grevilleas. We hope the use of this book will enable you to appreciate these relationships and increase your awareness of the amazing diversity and beauty of the world of Flowering Plants.

It is necessary to stress that this book does not present all there is to know about floral structure. It deals with the most common structural patterns and their variations, but some variations and exceptions are not included. The examples are drawn from plants common in gardens and the bush of south-eastern Australia, thus, many tropical families have not been mentioned. However, the principles of identification are not geographically confined and the basic information is applicable in any region. Having mastered the information presented here, the interested reader will have little trouble in working with plant identification manuals for other parts of the world.

Guidelines and conventions for pronunciation of botanical names can be found in Tasmanian plant names unravelled by Wapstra (et al., 2010), Plant names: A guide to botanical nomenclature by Spencer and coauthors (2007) and Western Australian plant names and their meanings by Sharr (1996). Actual practice varies, particularly from country to country. Sometimes it is the loudest voice that holds sway. The standard ending for family names (–aceae) is usually pronounced, in Australia, as ‘ay-see’. For example the Citrus Family Rutaceae = Ru-tay-see, and the Myrtle Family Myrtaceae = Mer-tay-see. Sometimes a slight extra emphasis is placed on the last syllable, effectively pronouncing both the ‘e’ and the ‘ae’. The standard ending for the names of orders (–ales) is usually pronounced ‘ay-lees’. Thus for the Citrus group, the order Sapindales = Sap-in-day-lees, and the order Myrtales which includes the Eucalypts = Mer-tay-lees.

Using this book

One way of finding out about floral structure and coming to grips with the terminology is to work through the book from the beginning, referring to living plants as often as possible. Throughout the text, important terms when first introduced appear in bold type. These terms are commonly encountered in books dealing with plant identification.

Another approach is to compare the labelled illustration or photograph of a fuchsia or a grevillea, for example, with flowers from the garden. It is usually not essential to have the exact plant illustrated; often a related species will be sufficiently similar. The illustrations are specifically intended as a visual aid to the type of flower structure commonly seen in the various families. In a number of cases, two or more species in a genus have been drawn, allowing an appreciation of the close similarity in structure at this level. (See Figs. 28–9, 48–50, 58–62, 84–8, 105–6.) Unfamiliar terms can be checked in the glossary, which will often refer to an illustrated example in the text. Many illustrations are included in order to show the application of terms in a wide range of examples.

Within the text, we have been selective when referring to figures and plates that illustrate a particular feature of plant structure. There may be more examples than the one(s) we have chosen.

In Chapter 8, families have been numbered in sequence purely for ease of navigation within this book. The numbers have no other relevance.

It must be remembered that, just like human beings, individual plants within a species often vary to some degree in their general appearance. Any attempt at neatly summarising the characteristics of a species (or genus or family) will almost certainly run the risk of overlooking unusual variations. Virtually all such comments relating to various plant groups possessing particular characteristics should be read as if preceded by the word ‘usually’.

Notes on the illustrations

The drawings in Chapter 8 were made from actual specimens, arranged to show as many relevant features as possible. To make comparisons easier, most flowers are drawn with the stalk at the bottom. This may not be how they would naturally appear on the plant and some mental adjustment may be necessary. The drawings are as accurate as possible, but some natural variation is likely—part of the experience of getting to know plants. Slight exaggeration has been necessary in a few cases to improve clarity, such as enlarging the gap between closely adjacent parts. Dashed lines usually indicate a part cut away to reveal the structure behind (e.g. Fig. 22b).

The transverse section (T.S.) of the ovary in each case has been drawn to illustrate the placentation. It may not be a true ‘section’, as some depth has occasionally been added to make parts more obvious.

In sections and half flowers (which are exact halves), the cut surfaces are unshaded, and the adjacent surfaces have usually been shaded to try to make this clear. Shading within the ovary represents the loculus or cavity that contains the ovules. Figure 21 shows the way in which the flowers were cut to give the views drawn in most of the illustrations.

Labelling has occasionally been omitted from parts of drawings and photographs that were difficult to pinpoint accurately or clearly. In some cases, a composite structure, for example, the ovary, is difficult to label with a single arrow. Reference to the diagrams in Chapter 2 should clarify this.

The captions for Figures 22–132 begin with the botanical name, in italics, of the species illustrated, followed by the common name (in parentheses) if one is available. Usually a floral formula is included which summarises the basic floral structure shown in the drawing. These formulae are explained at the end of Chapter 2. The short descriptions of the plant together with the illustration, should provide enough information to enable the species to be ‘identified’ for practice in working with keys. This procedure is explained in Chapter 7.

The magnification of each part of an illustration is included at the end of the caption. Measurements made on the drawings, when divided by the magnification, will give the real dimensions. This will sometimes be very small—the ovary in Leucopogon virgatus (Fig. 106), for example, is about half a millimetre across.

The captions for the plates follow a similar pattern except that magnifications have been omitted—measurements given in the description will give an idea of size. Floral formulae are not included if details of the flower are not visible.

There are many ways in which the various flower parts can be arranged to make up the structure we recognise as a ‘flower’. This chapter sets out to describe the structure of a simple flower, and then discusses some of the variation commonly encountered. Chapter 8 includes some more complex examples.

Floral structure is described under the following headings:

Structure of a basic flower

The perianth

The reproductive organs

Variation in floral structure

Arrangement and union of parts

The perianth

The calyx

The corolla

Symmetry

Aestivation

The reproductive organs

The androecium

The gynoecium

Placentation

The style and stigma

Discs and nectaries

Relationships of parts in the flower

The floral tube

Number of parts per whorl

Unisexual flowers

The floral formula

Structure of a basic flower

A basic flower (Fig. 1; Pl. 1) has four series of parts arranged in concentric whorls (or rings) on the receptacle, which is the name given to the expanded end of the pedicel (flower stalk). The two outer whorls are together known as the perianth, and are not directly involved in reproduction. The reproductive structures are located in the inner whorls.

The perianth

The outer whorl, known as the calyx, is composed of two or more parts called sepals, which are often green in colour and enclose the rest of the flower in the bud stage. Inside the calyx is the corolla, made up of petals, which are usually white or brightly coloured. It is usual for the sepals and petals to be equal in number.

The reproductive organs

A whorl of stamens, called the androecium, lies inside the corolla, and is generally taken to represent the male part of the flower. Each stamen has a slender filament (stalk) and, at the top, an anther in which the pollen is produced. The pollen grains carry the male reproductive units.

In the centre of the flower is the gynoecium, made up of carpels. Each carpel usually has three parts: an expanded basal part called the ovary, in which the ovules are produced; a central stalk-like section called the style; and a terminal stigma. The ovules contain the female egg-cells and the stigma surface is specially adapted to receive compatible pollen. The ovules, after fertilisation and further development, become seeds and the mature carpels with the enclosed seeds develop into the fruit. The gynoecium is generally regarded as the female part of the flower.

Figure 1b illustrates an expanded flower with the various whorls separated from each other. This places the receptacle at the bottom of the diagram, with the other parts laid out in sequence moving from the outside to the centre of the flower. Figure 1a shows the flower from above and illustrates the way in which the parts in adjacent whorls usually alternate with one another. The same flower is illustrated from the side in Figure 1c.

Variation in floral structure

Much of the variation in floral structure is embodied in four aspects:

•the number of whorls present (sometimes one or more whorls are absent)

Fig. 1 Structure of a basic flower: a from above; b expanded flower, showing the series of parts; c side view.

•the number of parts in any whorl

•the degree of union of parts, either within a particular whorl or between adjacent whorls

•the position of the ovary with respect to the other parts.

Arrangement and union of parts

Although the majority of species have their flower parts arranged in whorls, others have numerous parts arranged spirally on a more or less elongated receptacle, for example, in the genera Magnolia (Fig. 22) and Liriodendron (Pl. 6a–d).

Parts within a whorl may be united by their adjacent margins into a more or less single structure. The petals for example may be united into a tube-like form (Fig. 2j, k). The degree of union may only be small, or incomplete, for parts still to be considered united; for parts to be taken as free they should be completely so (and each then generally falls individually from the receptacle as the flower ages). Some texts use the term distinct instead of free.

The perianth

The calyx

The sepals may be separate from one another as in Figure 1 or wholly or partly united (Fig. 99; Pls. 14b, 21b). Sometimes an extra ring of sepal-like segments is attached outside the true calyx. This is known as an epicalyx and is typical of the genus Hibiscus (Pl. 21h) and of some other members of the family Malvaceae (Fig. 99; Pl. 21). Sometimes the sepals fall as the flower opens, as, for example, in