Six Families of Flowering Plants

Six globally–important families of flowering plants (two eudicots, four monocots)

Eudiocot Families:

  • Fabaceae/Faboidae = Peas

  • Asteraceae = Daises

Monocot Families:

  • Orchiadaceae = Orchids

  • Poaceae = Grasses

  • Liliaceae = Lillies

  • Iridaceae = Irises

The Naming of Plants (Taxonomic Principles)

  • Philosophical roots (Origins)

    • Plato → “essence” of natural kinds

    • Aristotle’s Historia\;Animalium applied classification to animals

    • Theophrastus (pupil of Aristotle)

    • Historia\;Plantarum & De\;Causis\;Plantarum – first systematic plant treatises

  • Pre-Linnaean descriptive phrases (polynomials) illustrated by genus Veronica examples:

    • Veronica floribus spicatis, foliis ternis – “flowers spiked, leaves pinched”

    • …long multi-word diagnoses common & unwieldy

  • Carl Linnaeus (1745–1753)

    • Introduced dual (binomial) nomenclature → genus + specific epithet

    • e.g. pre-Linnaean Rosa carolina fragrans, foliis medio tenus serratus became Rosa carolina

    • Separated name from description (description published elsewhere)

    • Easier for students, enabled universal catalogue

  • Modern arrangement tries to mirror phylogeny

    • Angiosperm Phylogeny Group (APG IV, 2016) – ~400 families recognised; names & boundaries updated regularly

Global Species Richness – Largest Plant Families

  • \text{Orchidaceae} ≈ 28,000 spp.

  • \text{Asteraceae} ≈ 32,000 spp. (some sources 22,700)

  • \text{Fabaceae} (combined subfamilies) ≈ 18,000 spp.

  • \text{Rubiaceae} ≈ 13,100 spp.

  • \text{Poaceae} ≈ 10,000 spp.

Eudicot Families (~aceae)

1. Fabaceae / Faboideae – “Pea & Bean Family”

  • Systematics

    • Now treated as one family with three subfamilies

    1. Faboideae – \sim 12,000 spp., → classic pea flowers

    2. Mimosoideae (formerly Mimosaceae)

    3. Caesalpinoideae (formerly Caesalpiniaceae)

  • Floral plan

    • Standard (banner): large upper posterior petal

    • Wings: two lateral petals

    • Keel: two partially fused lower petals enclosing stamens & pistil

    • Calyx usually 5 lobes; stamens often 10 (formula for sweet-pea: K(5)\;C(2),3\;A(9),1\;G1)

  • Vegetative traits

    • Leaves commonly compound/trifoliate, often with stipules; Australian members frequently shrubs, climbers, herbs rather than trees with obvious trifoliates

  • Diversity & distribution

    • Worldwide: \sim 500 genera, \sim 12,000 spp. (Faboideae)

    • Australia: \sim 140 genera, \sim 1,100 spp.

    • Iconic natives: Daviesia, Hovea, Pultenaea, Hardenbergia, Kennedia, Swainsona (incl. Sturt’s Desert Pea Clianthus formosus – floral emblem of SA)

  • Ecology

    • Symbiosis with nitrogen-fixing bacteria (Rhizobium) → root nodules → “green manure” in agriculture

  • Human uses

    • High-protein seeds & pods: soybean, green/runner/snow/kidney beans, peas, lentils, faba/broad beans, chickpea, cowpea, tamarind, etc.

  • Weed issues (SE Qld examples)

    • Desmodium uncinatum – Silver-leaf desmodium

    • Macroptilium atropurpureum – Siratro

  • Horticultural natives (cultivation traits, seasons, wildlife value)

    • Hairy Bush-Pea (Pultenaea villosa)

    • Purple Bush-Pea (Hovea acutifolia)

    • Native Sarsaparilla (Hardenbergia violacea)

2 Asteraceae – “Daisy, Sunflower or Composite Family”

  • Inflorescence = capitulum/head

    • Numerous tiny florets sit on common receptacle → look like single flower

    • Surrounded by involucral bracts (phyllaries)

    • Two floret types

    • Ligulate (ray): 5 fused petals forming strap-like “petal” – often female/sterile

    • Tubular (disk): 5 fused petals forming tube – typically bisexual

  • Floral characters

    • 5 petals, 5 epipetalous stamens with anthers fused into tube around style

    • Ovary inferior, 1 locule with single ovule → fruit = achene (e.g. sunflower “seed”)

    • Pappus (modified calyx) aids dispersal (hairs, bristles, scales)

  • Life-forms: mostly herbs/shrubs; annual or perennial; adapted to many habitats

  • Diversity

    • Global: \sim 1,900 genera, \sim 32,000 spp.

    • Australia: \sim 290 genera, \sim 1,400 spp.

  • Human interactions

    • Food: artichoke (Cynara scolymus), lettuce (Lactuca sativa)

    • Spice: tarragon (Artemisia dracunculus)

    • Medicinal: absinthe (Artemisia absinthium)

    • Oilseed: sunflower (Helianthus annuus)

    • Ornamentals: asters, chrysanthemums, dahlias, everlasting daisies (Xerochrysum), Tagetes marigolds, Zinnia etc.

    • Weeds: thistles, dandelion (Taraxacum officinale)

  • Native ornamentals & garden performance (examples)

    • Cut-leaf Daisy (Brachyscome multifida) – year-round bloom, pots/ground-cover

    • Golden Everlasting (Xerochrysum bracteatum) – papery bracts, dried flowers

    • Yellow Buttons (Chrysocephalum apiculatum) – fast-growing, silver foliage

Monocot Families

3 Orchidaceae – “Orchid Family”

  • Size & distribution

    • Worldwide ≈ 880 genera, \sim 27,800 spp. (≈ 8\% of all angiosperms)

    • Greatest diversity in tropics; Australia >1,500 spp. in \sim 156 genera (esp. SE & SW regions)

    • Qld floral emblem: Dendrobium bigibbum → now Vappodes phalaenopsis (Cooktown Orchid)

  • Floral structure (diagnostic)

    • Zygomorphic

    • Perianth: 3 sepals + 3 petals; one petal (labellum/lip) enlarged, often colourful & spurred

    • Central column (fused stamens + style + stigma); ovary inferior

    • Pollen in pollinia; seeds tiny, dust-like – require mycorrhizal fungi to germinate

  • Economic significance

    • Vanilla flavouring from fermented capsules of Vanilla planifolia – anatomy: inferior ovary becomes “bean” (diagram labels: column, rostellum, anther)

    • Ornamental industry massive; tissue culture common

  • Local biodiversity examples (Griffith University forests)

    • Nodding Greenhood (Pterostylis nutans)

    • Pink Nodding Orchid (Geodorum densiflorum)

    • Slender Hyacinth Orchid (Dipodium variegatum)

  • Cultivation: hobby collections in kitchens, shade-houses, gardens

4 Poaceae – “Grass Family”

  • Ecological footprint

    • Cosmopolitan, represent ≈ 20\% of global vegetation cover; dominate inland Australia

    • Diversity: worldwide \sim 780 genera, \sim 12,000 spp.; Australia 151 genera / 1,062 spp. (with 35 endemic)

  • Human reliance – > 50\% caloric intake

    • Cereals: wheat, rice, maize/corn, oats, barley, rye, millet, sorghum

    • Sugars: sugarcane (Saccharum officinarum)

    • Woody bamboos (construction, fibre, food shoots)

  • Flower morphology (wind-pollinated → reduced, no showy petals)

    • Spikelet = basic unit; consists of one to many florets on a rachilla

    • Each spikelet subtended by two glumes (bracts)

    • Floret enclosed by lemma (lower bract) + palea (upper)

    • Lodicules (tiny scales) = reduced perianth; 3 stamens common; ovary superior, 2 feathery stigmas

    • Awns: bristle extensions from lemmas (aid dispersal)

  • Allergy & pollen

    • Wind-borne pollen causes hay fever; major culprits often exotic pasture grasses

  • Identification cues

    • Growth form (tuft, tussock, mat, bamboo-like, etc.)

    • Inflorescence architecture: panicle, spike, raceme/digitate, spatheate

    • Spikelet details – number/shape of glumes, awns, sterile lemmas, etc.

5 Liliaceae – “True Lily Family”

  • Distribution

    • Temperate zones; worldwide ≈ 4,000 spp. in 254 genera

    • Australia ≈ 200 spp. (many introductions); endemic genera include Thysanotus (fringe-lilies), Laxmannia, Stypandra, Arthropodium

    • Classic exotics: Lilium (lilies), Tulipa (tulips)

  • Habit & vegetative features

    • Mostly tufted perennial herbs arising from bulbs/rhizomes; leaves linear, often grass-like

  • Floral characters

    • Tepals 6 (often spotted/striped nectar guides) arranged 3+3; free or united

    • Stamens 6 (two whorls of 3)

    • Gynoecium: 3 fused carpels, superior ovary, 3 loculi

    • Fruit a capsule or berry; many ornamental cultivars (e.g. Oriental hybrid lilies)

6 Iridaceae – “Iris Family”

  • Biogeography

    • Cosmopolitan with centres in South Africa (Cape) & Central/South America

    • Many horticultural genera: Iris, Freesia, Gladiolus, Crocosmia; some naturalised/weedy in Australia

    • Economic: saffron spice from stigmas of Crocus sativus

  • Morphology

    • Herbaceous, often from corms/rhizomes; leaves equitant (fan-like), linear, two-ranked (distichous), edge-on to stem

    • Perianth petaloid 3+3; sometimes zygomorphic (e.g. Dietes)

    • Stamens 3 (one whorl)

    • Ovary inferior, 3 fused carpels; seeds often arillate