Flora
See also: Flora of the Houtman Abrolhos
Most of North Island is dominated by chenopod shrubs, generally less than a metre (3 ft) high. The beach vegetation is largely Spinifex longifolius (Beach Spinifex), Salsola kali (Prickly Saltwort), Atriplex cinerea (Grey Saltbush) and naturalised Cakile maritima (Sea Rocket). Stable dunes are vegetated by Atriplex paludosa (Marsh Saltbush), Scaevola crassifolia (Thick-leaved Fan-flower), Olearia axillaris (Coastal Daisy-bush), Myoporum insulare (Blueberry Tree) and Exocarpos sparteus (Broom Ballart). Sheltered areas behind dunes support Salsola kali and Myoporum insulare and also Nitraria billardierei (Nitre Bush), the last of these being the only plant on the island to grow over 1 1⁄2 m (5 ft) high. In areas where limestone is close to the surface, the vegetation consists of Pimelea microcephala (Shrubby Rice-flower), Spyridium globulosum (Basket Bush) and Acanthocarpus preissii.
The rim of the central plain is vegetated by a dense shrubland of Rhagodia baccata (Berry Saltbush), Atriplex paludosa and Threlkeldia diffusa (Coast Bonefruit). Nearer the centre, the vegetation consists of Frankenia pauciflora (Seaheath), Muellerolimon salicorniaceum and Tecticornia arbuscula (Bulli Bulli), although T. arbuscula is replaced by Tecticornia halocnemoides (Shrubby Samphire) where the soil is shallow. The most low-lying area of the central plain, south of the salt lake, is water-logged in winter; it is vegetated by a dense mat of Sarcocornia quinqueflora (Beaded Samphire), Sporobolus virginicus (Marine Couch) and Suaeda australis (Seablite).
The dune, limestone and salt lake vegetation communities on North Island are considered to have high conservation significance. The dune and limestone communities have high biodiversity, are highly sensitive to disturbance and regenerate slowly. The salt lake community is considered significant because of the rarity of salt lakes on offshore islands.
According to a survey published in 2001, the following vascular plants occur on North Island:
- Acanthocarpus preissii
- Actinobole condensatum
- Atriplex cinerea (Grey Saltbush)
- Atriplex paludosa (Marsh Saltbush)
- Austrodanthonia caespitosa
- Austrostipa crinita
- Austrostipa variabilis
- Avena fatua (Wild Oat) (naturalised)
- Brachyscome ciliaris
- Bromus arenarius (Sand Brome)
- Bromus diandrus (Great Brome) (naturalised)
- Bromus hordeaceus (Soft Brome) (naturalised)
- Bromus madritensis (Madrid Brome) (naturalised)
- Bulbine semibarbata (Leek Lily)
- Cakile maritima (Sea Rocket) (naturalised)
- Calandrinia calyptrata (Pink Purslane)
- Carpobrotus virescens (Coastal Pigface)
- Chenopodium murale (Nettle-leaf Goosefoot) (naturalised)
- Crassula colorata (Dense Stonecrop)
- Cynodon dactylon (Couch) (naturalised)
- Daucus glochidiatus (Australian Carrot)
- Dodonaea aptera (Coast Hop-bush)
- Enchylaena tomentosa (Barrier Saltbush)
- Eragrostis dielsii (Mallee Lovegrass)
- Erodium cicutarium (Common Storksbill) (naturalised)
- Erodium cygnorum (Blue Heronsbill)
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- Euchiton sphaericus
- Euphorbia tannensis
- Exocarpos sparteus (Broom Ballart)
- Ficinia nodosa (Knotted Club Rush)
- Frankenia pauciflora (Seaheath)
- Grevillea argyrophylla (Silvery-leaved Grevillea)
- Helichrysum luteoalbum (Jersey Cudweed)
- Hordeum murinum subsp. leporinum (Barley Grass) (naturalised)
- Hornungia procumbens (Oval Purse) (naturalised)
- Juncus bufonius (Toad Rush) (naturalised)
- Malva parviflora (Marshmallow) (naturalised)
- Melilotus indicus (naturalised)
- Mesembryanthemum crystallinum (Iceplant) (naturalised)
- Muellerolimon salicorniaceum
- Myoporum insulare (Blueberry Tree)
- Nicotiana occidentalis subsp. hesperis (Native Tobacco)
- Nitraria billardierei (Nitre Bush)
- Olearia axillaris (Coastal Daisy Bush)
- Parapholis incurva (Coast Barbgrass) (naturalised)
- Parietaria debilis (Pellitory)
- Phalaris minor (Lesser Canary Grass) (naturalised)
- Pimelea microcephala (Shrubby Riceflower)
- Plantago debilis
- Podotheca angustifolia (Sticky Longheads)
- Rhagodia baccata (Berry Saltbush)
- Rhagodia latifolia
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- Rostraria cristata (naturalised)
- Salsola kali (Prickly Saltwort) (naturalised)
- Sarcocornia quinqueflora (Beaded Samphire)
- Scaevola crassifolia (Thick-leaved Fan-flower)
- Schenkia australis (naturalised)
- Senecio glossanthus (Slender Groundsel)
- Senecio pinnatifolius
- Setaria dielsii (Diels' Pigeon Grass)
- Sonchus oleraceus (Common Sow Thistle) (naturalised)
- Spergularia rubra (Sand Spurry) (naturalised)
- Spinifex longifolius (Beach Spinifex)
- Sporobolus virginicus (Marine Couch)
- Spyridium globulosum (Basket Bush)
- Stackhousia sp.
- Suaeda australis (Seablite)
- Tecticornia arbuscula
- Tecticornia halocnemoides (Shrubby Samphire)
- Threlkeldia diffusa (Coast Bonefruit)
- Thysanotus patersonii
- Trichodesma zeylanicum (Camel Bush)
- Triglochin mucronata
- Triglochin trichophora
- Triticum aestivum (Wheat) (naturalised)
- Vulpia myuros (Rat's Tail Fescue) (naturalised)
- Wurmbea monantha
- Zygophyllum simile
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