The first step in identifying a plant is usually to ascertain the family to which it belongs. This can be a formidable task in a region such as southern Africa with some 230 families of seed plants, many with very diverse representatives. The readily available vegetative characteristics are usually not enough to distinguish families, and a knowledge of flower features is essential. In many families the flower structure has become modified to a lesser or greater extent, or flowers may be very small and hidden between bracts, such as in the grasses (Poaceae), or inside an almost completely closed flower receptacle, as in the figs (Moraceae). In the paragraphs below, a few ideas and data are given which may help to make the task of identifying families a little easier.
General hints
The systematic examination of a plant in order to establish the characteristics required for its identification is described in detail in Cullen (1997). A few sentences from his work concerning ovary and ovule features are quoted here because these are often particularly difficult to determine: 'In order to see how many cells [locules] the ovary contains, it is usually necessary to section it horizontally across the middle [the widest part]. Such a section will also generally show how many ovules there are in the ovary or in each locule, and, very often, the way they are attached to the ovary - the placentation, which is a very important characteristic in the identification of families. With some groups it may also be necessary to cut another ovary longitudinally (along a diameter) to see precisely how the ovules are attached. The cutting of ovaries....is an art that has to be mastered with practice, as the ovaries can be very small indeed. In general terms it is relatively easy to cut a transverse section, using a single-edged razor blade. Longitudinal sections can be difficult and troublesome. The flower (or just the ovary, if it is large enough) should be held between finger and thumb, with the flower in the same position as it was on the plant, with the stem end pointing outwards. A cut should then be made carefully through this, moving the blade downwards as the cut goes through the tissues. In this way, clean surfaces will be left and the ovary will not be squeezed or squashed, which will happen if a sawing motion of the blade is used. It is sometimes helpful to rub over the ends of cut sections with the tip of a broad, black, felt-tip pen. The water-based ink is absorbed by the cut surfaces, which therefore stain black, but it is repelled by the waxy surface of the ovules, which are pale green and stand out from the rest of the stained cut.' A note by Goldblatt & Manning (2000) at the beginning of their key to angiosperms is also relevant in this context: 'In checking placentation it is often easier to examine ovaries after fertilisation when they have swollen slightly.'
Characteristics found only in a limited number of families
Certain distinctive attributes encountered in some or all members of a limited number of families may prove helpful when identifying plants (G - GYMNOSPERMS; M - MONOCOTYLEDONS; all others - DICOTYLEDONS):
Water plants, free-floating or with floating leaves:
Alismataceae (M), Aponogetonaceae (M), Araceae (M), Cabombaceae, Crassulaceae, Droseraceae, Hydrocharitaceae (M), Lemnaceae (M), Lentibulariaceae, Limnocharitaceae (M), Lythraceae, Menyanthaceae, Nymphaeaceae, Onagraceae, Podostemaceae, Pontederiaceae (M), Potamogetonaceae (M), Scrophulariaceae, Trapaceae.
Water plants, with submerged stems and leaves:
Alismataceae (M), Aponogetonaceae (M), Callitrichaceae, Ceratophyllaceae, Cymodoceaceae (M), Droseraceae, Elatinaceae, Haloragaceae, Hydrocharitaceae (M), Hydrostachyaceae, Lentibulariaceae, Limnocharitaceae (M), Lythraceae, Najadaceae (M), Onagraceae, Podostemaceae, Potamogetonaceae (M), Ranunculaceae, Ruppiaceae (M), Scrophulariaceae, Zannichelliaceae (M), Zosteraceae (M).
Parasitic plants:
(1) without chlorophyll: Balanophoraceae, Convolvulaceae, Hydnoraceae, Lauraceae, Rafflesiaceae, Scrophulariaceae
(2) growing on aerial parts of trees and shrubs: Loranthaceae, Viscaceae.
Grasses and grass-like plants:
Cyperaceae (M), Juncaceae (M), Poaceae (M), Restionaceae (M), Typhaceae (M).
Succulent plants:
*Agavaceae (M), Aizoaceae, Amaranthaceae, Amaryllidaceae (M), Apocynaceae, Asphodelaceae (M), Asteraceae, Balsaminaceae, Begoniaceae, Boraginaceae (Heliotropium curassavicum), Cactaceae, Chenopodiaceae, Crassulaceae, Dracaenaceae (M), Euphorbiaceae, Geraniaceae, Goodeniaceae, Hyacinthaceae (M), Hydnoraceae, Lamiaceae, Lemnaceae (M), Loranthaceae, Menispermaceae, Mesembryanthemaceae, Molluginaceae, Orchidaceae (M), Passifloraceae, Pedaliaceae, Phytolaccaceae, Piperaceae, Polygonaceae, Portulacaceae, Rafflesiaceae, Rubiaceae (Phylohydrax), Scrophulariaceae, Viscaceae, Vitaceae, Zygophyllaceae.
Plants with true bulbs:
Alliaceae (M), Amaryllidaceae (M), Hyacinthaceae (M), *Liliaceae (M).
Plants with milky or coloured to conspicuous watery sap:
Alismataceae (M), Apocynaceae, Araceae (M), Asteraceae, Burseraceae, Cabombaceae, Campanulaceae, Convolvulaceae (some spp. of Ipomoea), Euphorbiaceae, Fumariaceae, Haemodoraceae (M), Limnocharitaceae (M), Lobeliaceae, Moraceae, Moringaceae, Nymphaeaceae, Papaveraceae, Sapotaceae.
Stems twining:
Achariaceae, Annonaceae, Apocynaceae, Aristolochiaceae, Basellaceae, Connaraceae, Convolvulaceae, Dioscoreaceae (M), Euphorbiaceae, Fabaceae, Flagellariaceae (M), Hyacinthaceae (M), Lauraceae, Linaceae, Luzuriagaceae (M), Malpighiaceae, Menispermaceae, Oleaceae, Polygonaceae, Solanaceae.
Tendrils present:
Achariaceae, Apocynaceae, Bignoniaceae, Colchicaceae (M), Cucurbitaceae, Fabaceae, Flagellariaceae (M), Fumariaceae, Linaceae, Menispermaceae, Passifloraceae, Rhamnaceae, Sapindaceae, Smilacaceae (M), Vitaceae.
Leaves absent or reduced to scales:
Amaranthaceae, Apocynaceae, Asparagaceae (M), Asteraceae, Bruniaceae, Burmanniaceae (M), Cactaceae, Campanulaceae, *Casuarinaceae, Chenopodiaceae, Convolvulaceae, Cucurbitaceae, Cupressaceae (G), Euphorbiaceae, Geraniaceae, Hyacinthaceae (M), Hydnoraceae, Juncaceae (M), Lauraceae, Lemnaceae (M), Mesembryanthemaceae, Orchidaceae (M), Podostemaceae, Rafflesiaceae, Restionaceae (M), Santalaceae, Scrophulariaceae, Viscaceae, Zannichelliaceae (M).
Leaves digitately compound (3 to many leaflets):
Anacardiaceae, Apiaceae, Araceae (M), Araliaceae, Arecaceae (M), Bignoniaceae, Bombacaceae, Burseraceae, *Cannabaceae, Capparaceae, Ceratophyllaceae, Cucurbitaceae, Cunoniaceae, Dioscoreaceae (M), Droseraceae, Euphorbiaceae, Fabaceae, Fumariaceae, Geraniaceae, Lamiaceae, Lentibulariaceae, Malvaceae, Oleaceae, Oxalidaceae, Passifloraceae, Pedaliaceae, Ranunculaceae, Rosaceae, Rutaceae, Sapindaceae, Sterculiaceae, Verbenaceae, Vitaceae, Zygophyllaceae.
Leaves paripinnate:
Araliaceae, Balanitaceae, Fabaceae (especially Caesalpinioideae), Hydrostachyaceae, Meliaceae, Oxalidaceae, Ptaeroxylaceae, Sapindaceae, Stangeriaceae (G), Zamiaceae (G) Zygophyllaceae.
Leaves imparipinnate:
Anacardiaceae, Apiaceae, Araceae (M), Arecaceae (M), Asteraceae, Bignoniaceae, Brassicaceae, Burseraceae, Connaraceae, Cunoniaceae, Fabaceae, Fumariaceae, Geraniaceae, Haloragaceae, Hydrophyllaceae, Hydrostachyaceae, Kirkiaceae, Meliaceae, Melianthaceae, Moringaceae, Oleaceae, Proteaceae, Ranunculaceae, Resedaceae, Rosaceae, Rutaceae, Sapindaceae, Stangeriaceae (G), Valerianaceae, Zamiaceae (G), Zygophyllaceae.
Leaves 2x or 3x pinnate:
Apiaceae, Araceae (M), Araliaceae, Asteraceae, Bignoniaceae, Fabaceae, Fumariaceae, Geraniaceae, Hydrostachyaceae, Lentibulariaceae, Meliaceae, Moringaceae, Proteaceae, Ranunculaceae.
Flowers densely crowded, sessile, usually small to minute; in heads, on a fleshy axis surrounded by a conspicuous bract, or enclosed as in a fig; inflorescence often resembling a single flower:
Amaranthaceae, Apiaceae, Araceae (M), Araliaceae, Asteraceae, Balanophoraceae, Bruniaceae, *Casuarinaceae, Colchicaceae (M), Convolvulaceae, Dipsacaceae, Eriocaulaceae (M), Euphorbiaceae (Euphorbia), Fabaceae (Mimosoideae), Gentianaceae, Hamamelidaceae, Hyacinthaceae (M), Juncaceae (M), Moraceae, Portulacaceae, Proteaceae, Rhamnaceae (Phylica), Rubiaceae, Thymelaeaceae, Urticaceae, Verbenaceae, Xyridaceae (M).
Flowers in an umbel or pseudo-umbel:
Agapanthaceae (M), Alismataceae (M), Alliaceae (M), Amaryllidaceae (M), Anthericaceae (M), Apiaceae, Apocynaceae, Araliaceae, Capparaceae, Cyperaceae (M), Euphorbiaceae, Fabaceae, Geraniaceae, Gisekiaceae, Hydrocharitaceae (M), Iridaceae (M), Limnocharitaceae (M), Loranthaceae, Malpighiaceae, Menyanthaceae, Molluginaceae, Myrsinaceae, Myrtaceae, Nyctaginaceae, Oxalidaceae, Ranunculaceae, Rhamnaceae, Ruppiaceae (M), Rutaceae, Smilacaceae (M), Solanaceae, Thymelaeaceae, Viscaceae.
Perianth absent:
Amaranthaceae, Araceae (M), Asteraceae, Balanophoraceae, Begoniaceae, Callitrichaceae, *Casuarinaceae, Chenopodiaceae, Cupressaceae (G), Cymodoceaceae (M), Cyperaceae (M), Euphorbiaceae, Fabaceae (Brachystegia), Gunneraceae, Haloragaceae, Hydrostachyaceae, Lemnaceae (M), Moraceae, Myricaceae, Myrothamnaceae, Najadaceae (M), Pinaceae (G), Piperaceae, Poaceae (M), Podocarpaceae (G), Podostemaceae, Potamogetonaceae (M), Restionaceae (M), Ruppiaceae (M), Salicaceae, Stangeriaceae (G), *Taxodiaceae (G), Typhaceae (M), Viscaceae, Zamiaceae (G), Zannichelliaceae (M), Zosteraceae (M).
Perianth dry, pergamentaceous:
Amaranthaceae, *Cannabaceae, *Casuarinaceae, Cyperaceae (M), Eriocaulaceae (M), Juncaceae (M), Moraceae, Plantaginaceae, Poaceae(M), Restionaceae (M), Typhaceae (M), Xyridaceae (M).
Perianth spurred:
Balsaminaceae, Brassicaceae, Lentibulariaceae, Orchidaceae (M), Pedaliaceae, Scrophulariaceae, Valerianaceae, Violaceae.
Sex organs, at least of one sex, in cones or catkins:
*Casuarinaceae, Cupressaceae (G), Euphorbiaceae, *Fagaceae, Gunneraceae, Moraceae, Myricaceae, Myrothamnaceae, *Pinaceae (G), Podocarpaceae (G), Salicaceae, Stangeriaceae (G), *Taxodiaceae (G), Welwitschiaceae (G), Zamiaceae (G).
Anthers connate:
Apocynaceae, Araceae (M), Asteraceae, Balsaminaceae, Cucurbitaceae, Fumariaceae, Gentianaceae, Hydnoraceae, Lobeliaceae, Rafflesiaceae, Scrophulariaceae, Violaceae.
Gynoecium of 2 or more free carpels with separate styles:
Alismataceae (M), Annonaceae, Aponogetonaceae (M), Arecaceae (M), Cabombaceae, Connaraceae, Crassulaceae, Cymodoceaceae (M), Gisekiaceae, Juncaginaceae (M), Limnocharitaceae (M), Menispermaceae, Nymphaeaceae, Phytolaccaceae, Potamogetonaceae (M), Ranunculaceae, Rosaceae, Ruppiaceae (M), Zannichelliaceae (M).
Fruit a circumscissile capsule; opening by a lid:
Aizoaceae, Hypoxidaceae (M), Lentibulariaceae, Lythraceae, Plantaginaceae, Plumbaginaceae, Portulacaceae, Primulaceae, Sphaenocleaceae.
