Biology Of Australian Fauna & Flora 4-6

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Xeromorph

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A plant that has a form (morph) that enables it to live in dry & stressed environments

Increased aridity, increased fire frequency and weathering of soils during the last 30 my favoured the evolution and dominance of xeromorphs

• Two types: succulents and sclerophylls

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Succulent plants

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Plants fleshy, with cells large & filled with watery sap; drought and salt tolerant

•Often reduced leaves, stem photosynthetic •Family Chenopodiaceae (saltbushes) of deserts; related to coastal saltmarsh plants

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Adaptations: Chenopod shrub, Atriplex (saltbush or bluebush)

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Surface colour reflects radiation

•Covered with bladder cells to excrete salt

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Sclerophylls - hard-leaved plants

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More common than succulents

•e.g Family Proteaceae Banksia - tough rigid leaves that do not wilt when water stressed

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Adaptions of Sclerophylls

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Often small leaf size, short internodes

• Proportionally thick leaves

• Reduced surface area/volume ratio

Anatomical features Thick-walled cells (sclereids, fibres) - lignin in walls Thick cuticle and waxy coating

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Why might sclerophylly be an adaptation to low nutrient soils?

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Lack of nutrients can limit plant cell growth and metabolism, e.g., P is critically important, as backbone of nucleic acids, in ATP, cell membranes etc.

•slow growth, smaller leaves and internodes, carbohydrates channeled into lignin, thick cell walls = more efficient use of nutrients

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Many sclerophylls adapted to surviving fire

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Effects of fire depend on temperature and duration (speed) of fire: very fast hot fire may do less damage than a slow long fire !Plant adaptations include:

1.Tolerance of fire: protective features, even stimulated by fire to flower

2.Adult plant killed but seeds survive

3. Plants promote fire e.g. eucalypts with oil in leaves help fire to burn rapidly (less damage)

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Adaptations to tolerating fire

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Thick fibrous outer bark (corky layers) protects living parts - phloem and cambium

1. Aerial: epicormic

2. Underground buds Lignotubers (eucalypts)

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Fire as management tool to maximise biodiversity

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Burn too often (<5 year cycle), plants killed, grow from seed but cannot reach flowering age and set seed; only short-lived plants or sprouter with bulbs, rhizomes survive !

Long-time unburnt (>50 yrs), some shrubs die & some grow large and dominate, shading out smaller plants

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Biology of family Proteaceae

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Forests, woodlands, heathlands on low nutrient soils e.g. Banksia, Grevillea

•Rainforests Macadamia, Telopea(waratahs) •Sclerophyll woody shrubs and trees with corky bark, often lignotubers

•Fruits woody follicles or fleshy drupes

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The typical Proteaceae flower

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Grevillia

4-lobed perianth (tepals)

• 4 stamens attached to tepals

• Ovary 1 or 2 compartments

• Style long & acts as pollen presenter (male phase) then receives pollen (female phase)

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Banksia - fruits, seeds and fire (proteaceae)

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Often only a few ovaries develop as fruits ! Fruit a woody follicle, usually opens after fire !

2 winged seeds per follicle !

A ‘separator’ holds seed in place until after fire & rain - swells and pulls seed out

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Australian Legumes (Fabaceae)

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Three families:
Peas (Fabaceae)
Wattles (Mimosaceae, Acacia)
Cassias (Caesalpiniaceae)
Fruits a pod - a legume! Food plants - peas and beans

Native species often toxic but used by Aborigines
Some a source of medicinal compounds or genetic traits (e.g. drought tolerance) for crop legumes e.g. Glycine traits for soy beans

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Australian Fabaceae

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Peas

Seeds have hard resistant coats - survive fire Leaves often compound - 3 leaflets or more

Sclerophyll forms leaves simple, reduced to spines or scales

Nitrogen fixing

‘Egg & bacon peas’ Insect pollinated

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Acacia (Mimosaceae) the Wattles

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Known in Australia since the Early Miocene

Acacia is the largest genus of woody flowering plants in Australia with 960 species

Occur in rainforests and wet eucalypt forest e.g. Acacia melanoxylon (blackwood

Dominant in semi-arid and arid regions e.g. mulga lands

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Acacia fruits and seeds

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Fruit a legume (pod)

•seed coat hard - seed won’t take in water and germinate until this is cracked (e.g. by heat of fire)

•often have an eliasome - ants take seeds underground

Keep plant relatively free of fungal spores

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Family Myrtaceae

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In Australia: bottlebrushes, tea trees, paperbarks, lilly pillies; eucalypts dominate forests and woodlands

Used traditionally for wood for canoes, bark, honey, water

Modern uses- horticulture, timber, paper, oils, spices - cloves

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Characteristics of Family Myrtaceae

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All have leaves with aromatic oils in oil glands •Anti-herbivory; increases flammability

Dry-fruited forms e.g. eucalypt capsule opens by valves (splitting of top of ovary)

Fleshy-fruited forms e.g. rainforest lilly pilly

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Myrtaceae typical flower

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Flower regular in shape, 4-5 sepals, 4-5 petals Tea tree

Many stamens ! Inferior ovary

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The eucalypts

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700+ species in Australia

Forest, woodlands and mallee shrublands

All habitats except rainforest, alpine and arid desert

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Mountain ash!Eucalyptus regnans

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The tallest flowering plant in the world "100+ m height, 400 years old, nest hollows a resource for animals""After fire, regenerates from seed stored in canopy in woody fruits

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Eucalypts have distinctive foliage at various life stages

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Eucalyptus adult leaf isobilateral anatomy!

Juvenile: often leaf opposite, sessile, held horizontally, dorsiventral anatomy

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Identifying eucalypts!

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Fruit shape and size

•Bark type

•Leaf shape and size (including juveniles)

•Flower bud shape/number