THE PLANT KINGDOM (UNIT 1) Lesson 1 CLASSIFICATION OF PLANTS AND THE PLANT NAMING SYSTEM Aim Describe the classification of higher plants. Name the main plant groups; outline their characteristics and life cycles. BOTANICAL/HORTICULTURAL NOMENCLATURE Plants are generally given two different types of names: common names and scientific names. Common English language names usually given to plants by amateur gardeners as a Names descriptive, easy-to-remember tag. Many plants have more than one common name, and sometimes the same common name can be given to several quite different plants. This, along with the fact that there is no real control over common names, makes them inaccurate and unreliable for plant identification. Scientific Based on the Latin language, these names often seem more complex than Names common names at first glance; however, they have a system to them which can make plant identification much easier. The system of scientific naming is strictly controlled and coordinated by botanists throughout the world. Scientific names should always be used in preference to common names. Much of the Latin in scientific plant names will describe certain characteristics about a plant, thus, knowledge of Latin can be of help when studying plant names but it is not essential. The Binomial System The scientific plant names, which you see in books or on plant labels in a nursery, usually consist of two words. This is called the binomial naming system: e.g. Azalea indica Azalea indica The first word is the genus name of the plant. The second word is the species name of the This word starts with a capital letter. plant. In general, this word starts with a lower- case letter. There are exceptions to this rule - some people capitalise the first letter of a species name where a species has been named after a person or country. However in recent years this is no longer the accepted way to write a species name and now all species name irrelevant of whether it is a name or not start with a lower case letter. 1 When writing a scientific name of a plant, it is conventional to either italicise or underline both words in the name e.g. Azalea indica or Azalea indica . (Italicising is more common.) Botanical Classification In the scientific system, plants are classified by dividing them into groups, which have similar characteristics. These groups are then divided into smaller groups with similar characteristics. The smaller groups are divided again and, so, the division of group to sub-group and sub-group to further sub-groups goes on, until finally you have only one type of plant in each group. The two major groupings of organisms are kingdoms: the plant kingdom and the animal kingdom. Following this, the main levels of divisions of plants are: All plants are divided into PHYLA (singular: phylum) Phyla can be divided into DIVISIONS Divisions are divided into CLASSES Classes are divided into ORDERS Orders are divided into FAMILIES Families are divided into GENERA (singular: genus) Genera are divided into SPECIES Species are sometimes divided into VARIETIES Although there are many levels of division, the main ones we work with are at the lower end of the divisional scale: family, genus, species and variety/sub-species. Horticultural Phyla The main plant phyla we are concerned with in horticulture are: • Anthophyta (i.e. angiosperms). This group includes all plants that produce flowers, e.g. eucalypts, roses, lettuce, grasses. They are seed-bearing plants. • Coniferophyta (i.e. gymnosperms - conifers). This includes all plants that produce cones, e.g. pines, cypress, junipers. They are naked seed-bearing plants. • Pterophyta (i.e. ferns). This includes plants that reproduce by spores rather than seeds. 2 Other phyla include such things such as mosses, fungi, bacteria and algae. Anthophyta is divided into two classes: 1. Dicotyledonae . In these plants the first leaves to appear from a germinating seed are in a pair (two leaves appear at once). In general, the veins in the leaves of dicotyledons are reticulate not parallel (e.g. pea, eucalypt). Dicotyledons (commonly called dicots) also tend to have a taproot with lateral branches, as opposed to a fibrous root system. Note: Reticulate venation is when the main veins on the leaves branch out; with smaller veins arising from the larger ones. 2. Monocotyledonae . In these plants the first leaf to appear when a seed germinates is a single leaf. In general, the veins in the leaves of monocotyledons are parallel to each other extending up the leaf (not spreading). Monocotyledons (commonly call monocots) also tend to have a fibrous root system, as opposed to a taproot with lateral branches. Grasses, irises and orchids are examples of monocots. SELF ASSESSMENT Perform the self assessment test titled ‘Self Assessment Test 1.1’. If you find yourself getting the answers wrong, revise the notes from this lesson and repeat the test. Plant Families and Species It can be seen above that you can distinguish between dicotyledons and monocotyledons by a couple of very simple characteristics. In the same way, we can usually distinguish which family a plant belongs to by a few basic characteristics. For example: • Lamiaceae family: foliage is perfumed, stalks are four-sided (i.e. square-shaped) and flowers have two distinct lips (e.g. Mint Mentha spp.). • Araceae family: leaves are usually heart-shaped and the plants commonly originate in tropical regions (e.g. Philodendron ). • Asteraceae: plants in this family have ‘daisy’ flowers (e.g. Chrysanthemum ). needs italics • Apiaceae: flowers occur in an umbrella-like head on a single stalk (e.g. Parsley Petroselinum spp.). You should be able to tell a family name from other types of names by the fact that it will end with "aceae". Genus names do not end in ‘ aceae’ . For example: Eucalyptus ficifolia Eucalyptus is the genus, ficifolia is the species The family this plant belongs to is the Myrtaceae family. 3 Sometimes a third word (and perhaps a fourth) is added to follow the species. These words refer to the variety of that particular species. For example: Acer palmatum var. dissectum Atropurpureum Group Acer is the genus palmatum is the species dissectum tells us this is a variety of Acer palmatum with dissected leaves. Atropurpureum Group tells us this variety belongs to a group of Acer palmatum var. dissectum that have purple foliage. 4 Sub Species Sub-species are a naturally occurring geographical variant of a species – in order it is a taxonomic rank directly below species. Subspecies names are either recognised by the abbreviation subsp. or ssp. (not to be confused with spp. which is explained below). For example: Acacia terminalis ssp. terminalis See above: all the words in a plant name that includes a subspecies are in italics - other than the abbreviation for sub-species. Note: the abbreviated term spp. (meaning: species plural) refers to all the species in that genus and is sometimes used when the writer is referring to most of the species in that genus (i.e. for example Rosa spp. meaning (generically) all rose species). A writer might say “Rosa spp. are prone to black spot”; they may know that many species are not prone to black spot but because so many are they do not want to write a definitive list. If you see the abbreviated term sp. (species) it means that the writer is referring to a single unknown species within a known genus e.g. “I saw a beautiful plant – a Rosa sp.” Hybrids, Varieties and Forms You may be confused by the difference between hybrids, varieties, forms and cultivars. A hybrid plant is one which has resulted from two different species cross breeding. The parent plants are almost always in the same genus. Most hybrids are deliberately bred by humans, although some occur in nature where the distributions of the two parent species overlap. For example, Eucalyptus ‘Torwood’ is a cross between Eucalyptus torquata and Eucalyptus woodwardii . Sometimes the two plants which have been cross bred are both mentioned and an "x" is placed between them, e.g. Eucalyptus torquata x woodwardii. If a plant is a cross between two genera then it would be depicted (for example) as follows: x Cupressocyparis leylandii A variety (shown in a botanical name as var.) or form (shown as f) is a particular type of naturally occurring plant in one species. It displays minor variation/s from the typical species for example: a variety may be larger than the typical species plant; a form may have lesser difference e.g. it may have a cream instead of yellow flower). A variety (correctly known as varietas) of form (correctly known as forma) do not have parents from two different species, but a hybrid does. Examples of how to correctly depict variety and form in a botanical name: Gleditsia tricacanthos var. inermis Malva moschata f. alba Note: variety and form names are written in italics and start with a lower case letter. The abbreviations var. and f. should not be italicised. Cultivars The word cultivar is derived from the words cultivated variety . The accepted meaning of the word cultivar varies somewhat. In general, a cultivar is a group of cultivated plants (bred by people i.e. not a natural variant like a variety or form) that are clearly distinguishable from others by a certain characteristic (for example a certain flower colour, leaf colour or shape etc.). This characteristic must be passed on to the offspring (whether produced sexually or asexually) of the plant for it to be a true cultivar. In some countries, the word cultivar means the same thing as a variety (but this is not botanically accurate).