Visits by botanists to the shores of Port Phillip Bay date from as early as 1802 (Robert Brown with Matthew Flinders). However, the vegetation surrounding the bay, and in particular that of greater Melbourne, has been studied only sporadically. Hortus Victoriensis, the first published record of the plants of the Port Phillip area, was produced by an English gardener, Daniel Bunce, in 1851. Despite the wide coverage of the State by the most significant 19th-century Australian botanist, Ferdinand von Mueller, sadly nothing appears to have been published by him specifically referring to the plant life that occurred near to his residence at South Yarra, near Melbourne's centre. The most extensive publication on the vegetation of Melbourne, by the late J.H. Willis, did not appear until 1966. His work drew on his comprehensive personal knowledge of the area and his familiarity with historical records, both in the form of plant specimens held at the National Herbarium (where he spent most of his working life) and in the written works of earlier botanists and naturalists. The flora of the Merri Creek in the 1890s was described by H.M.R. Rupp; the Cheltenham area, the basalt plains and the salt marshes in 1933-35 by R.T. Patton (in Proceedings of the Royal Society of Victoria); the Mitcham area in 1937 by J.W. Audas ('Excursion to Mitcham', Victorian Naturalist, vol. 54); the lower Yarra River in 1911 by J. Tovey ('Some notes on Coode Island and its flora', Victorian Naturalist, vol. 28); and the flora of Sandringham and Keilor plains in 1911 and 1916 by C.S. Sutton ('Notes on the Sandringham flora', Victorian Naturalist, vol. 28; 'A sketch of the Keilor Plains flora', Victorian Naturalist, vol. 33). Numerous other articles and foray lists concerning Melbourne's flora have been published in the journal of the Field Naturalists' Club of Victoria. Little has been recorded of the cryptogamic plants (mosses, lichens and fungi) of Melbourne.
Greater Melbourne had diverse plant communities, which reflected the soil types, aspect and rainfall in the region. The richness of the vegetation was largely the result of the location of the city on the junction of three major geological formations: the fertile clay soils of the basalt plain formed by late Tertiary and Quaternary lava flows from volcanoes to the west and north-west; the hillier country of generally poor, strongly weathered soils derived from Silurian sediments north and east; and the sandy plains of Tertiary origin to the south-east of the city.
Immediately west and north-west of the present Central Business District, the Keilor volcanic plains supported a rich and diverse flora. In drier parts of the plain, grasslands dominated by kangaroo grass (Themeda triandra) were extensive and contained a wealth of colourful herbs such as lemon beauty-heads (Calocephalus citreus), common everlasting (Chrysocephalum apiculatum), bindweed (Convolvulus angustissimus), blue devil (Eryngium ovinum), scaly buttons (Leptorhynchos squamatus), feather-heads and pussy-tails (Ptilotus macrocephalus and Ptilotus spathulatus respectively). Many of these are now exceedingly rare, and a number of highly localised herbs (such as button wrinklewort, Rutidosis leptorrhynchoides, and sunshine diuris, Diuris fragrantissima) are almost extinct in the wild. Wetter sites on the plain were dominated by closed grasslands of common tussock (Poa labillardierei). Surveys by William Darke and others from the 1840s, however, show that large strips of this plain carried woodland, dominated by drooping she-oak (Allocasuarina verticillata) and the now almost extinct tree form of silver banksia (Banksia marginata), with river red gum (Eucalyptus camaldulensis) along creeks and in occasional scattered clumps. Grassy woodland of river red gum, drooping she-oak and yellow box (Eucalyptus melliodora) occurred on the strip of soil derived from tertiary basalt that runs from Tullamarine through Essendon to the centre of Melbourne and on the volcanic plains from Tullamarine to Broadmeadows. Grey box (Eucalyptus microcarpa), yellow gum (Eucalyptus leucoxylon) and hill manna gum (Eucalyptus viminalis subspecies viminalis) also occurred on better drained sites, such as on Gellibrand Hill.
The vegetation of the coastal foreshore on the eastern side of Port Phillip was largely scrub dominated by drooping she-oak and coast banksia (Banksia integrifolia), with an understorey of coast tea-tree (Leptospermum laevigatum), seaberry saltbush (Rhagodia candolleana), coast beard-heath (Leucopogon parviflorus) and bower spinach (Tetragonia implexicoma). The primary sand dunes were also vegetated with coastal tussock grassland (mainly Poa poiformis and Austrostipa stipoides), with creeping spinifex (Spinifex sericeus) and coast saltbush (Atriplex cinerea) locally common. Behind the primary dunes there was a more diverse patchwork of wattle and tea-tree scrub, and tea-tree heath on damper sites.
Inland of the foreshore communities, coastal plains grassy woodland of drooping she-oak stretched from beyond Frankston nearly to the mouth of the Yarra. To the east, as far as Cranbourne and Hastings, the woodland was dominated by coast manna gum (Eucalyptus viminalis subspecies pryoriana) and mealy stringy-bark (Eucalyptus cephalocarpa). Black she-oak (Allocasuarina littoralis) occurred in this woodland on wetter sites, and drooping she-oak on drier sites. Hedge wattle (Acacia paradoxa) was a common understorey shrub, along with cherry ballart (Exocarpos cupressiformis) and black wattle (Acacia melanoxylon). Lower lying areas were tea-tree heath dominated by prickly tea-tree (Leptospermum continentale and Leptospermum scoparium) and wattle and tea-tree scrub dominated by silky tea-tree (Leptospermum myrsinoides) and coast wattle (Acacia longifolia subspecies sophorae). Remnants of these heath lands and heathy woodlands (now surviving in Cheltenham, Clayton and, until the 1970s, railway verges at Oakleigh) were rich in ground orchids, with numerous species of Caladenia, Diuris, Thelymitra and Pterostylis. On clayier soils, especially on flat-topped ridges, grassy woodlands of yellow box, river red gum, lightwood (Acacia implexa) and a tall form of sweet bursaria (Bursaria spinosa) dominated. Remnants of this community exist in St Kilda (Alma Park), South Yarra (Royal Botanic Gardens) and Highett. It is likely that the pioneer species coast tea-tree, coast wattle and hedge wattle have become invasive weeds in disturbed sites since European settlement because of large-scale disruption of the vegetation between the foredunes and the woodland and heath land communities.
Former high sea levels had left a number of land-locked salt marshes stretching between Altona and Albert Park. The largest of these was the former West Melbourne Swamp. They supported plant communities of salt-tolerant plants such as beaded glasswort (Sarcocornia quinqueflora) and creeping brookweed (Samolus repens) on swampier ground, and chaffy saw-sedge (Gahnia filum) and rounded noon-flower (Disphyma crassifolium) on higher ground. Australian saltmarsh-grass (Puccinellia stricta) and Australian salt-grass (Distichlis distichophylla) would have also occurred around the margins of the marshes. On the alluvial flats near the mouth of the Yarra, there occurred an extensive salt marsh system, including lignum (Muehlenbeckia florulenta) on the less saline sites. Fragments of the salt marsh remain beneath the West Gate Bridge, but the nearest occurrence of lignum is now at Laverton. There is debate about whether mangroves (Avicennia marina) occurred along the lower Yarra. There is no firm evidence of their occurrence there, but a small colony survives near the mouth of the nearby Kororoit Creek. This colony was almost destroyed by an extensive oil spill from an adjacent refinery in 1950. Mangroves were planted in the Stony Creek backwash (on the west bank of the Yarra, immediately upstream of the West Gate Bridge) in the 1980s and have thrived at that site since.
Just north-east of the city, on basalt soils stretching from Fitzroy to Fairfield, was grassy woodland dominated by river red gum, drooping she-oak and black wattle, with some yellow box. Since early records mention that grass was 'waist-high' north of the settlement, it was probably dominated by common tussock-grass and spear-grasses (Austrostipa species) rather than kangaroo grass.
The lower Yarra supported a riparian vegetation dominated by river red gum, with swamp paperbark (Melaleuca ericifolia) occurring on marshy areas such as immediately west of the city, near the Botanic Gardens (where some remnant stands remain), and in the billabongs of Kew and Bulleen. East of the Yarra at Studley Park is a mixture of woodland associations dominated by yellow gum, yellow box, river red gum or hill manna gum. Much of Kew and Camberwell were covered by grassy woodland of river red gum and yellow box. In Bulleen and Templestowe some of the hillsides were covered with black she-oak, silver banksia and hill manna gum. From Box Hill to the Dandenong Ranges, woodland was dominated by mealy stringy-bark and yellow box. Long-leaf box (Eucalyptus goniocalyx) and red stringy-bark (Eucalyptus macrorhyncha) occurred on drier (mostly northern and north-western) slopes, and narrow-leaf peppermint (Eucalyptus radiata) and messmate (Eucalyptus obliqua) occurred on wetter sites, especially in the foothills around the base of Mount Dandenong. The understorey was dominated by burgan (Kunzea ericoides sensu latero), blackwood, cherry ballart and sweet bursaria. Wetter sites in the eastern suburbs supported tea-tree heath dominated by prickly tea-tree; creeks and drainage lines were vegetated with swamp gum (Eucalyptus ovata) and swamp paperbark.
On shallow soils from Doncaster to Warrandyte and north to Yarrambat and Panton Hill, the foothills were covered with woodlands dominated by red box (Eucalyptus polyanthemos) and red stringy-bark. Better soils, especially from North Croydon to Lilydale, supported yellow box and candle bark (Eucalyptus rubida) woodland, with scattered patches of narrow-leaf peppermint open forest. In Templestowe, the dominant eucalypt of tall open forest along the Yarra changes from river red gum to manna gum.
Flatter parts of the Mornington Peninsula on silty soils from Moorabbin to Cranbourne were dominated by river red gum and blackwood with scattered black wattle. Creeks in this region were vegetated with swamp paperbark and swamp gum. Along creek lines and fringing swamps on sandy soils, scented paperbark (Melaleuca squarrosa) occurs with or replaces swamp paperbark.
Many plants were used by indigenous people in Melbourne. The most important vegetable foods in south-eastern Australia were derived from underground storage organs. Victorian Koories used roots and tubers from a wide range of species, especially orchids and lilies, and around billabongs or saline swamps, they used cumbungi (Typha species), water ribbons (Triglochin procerum) and the sedges Bolboschoenus medianus and Bolboschoenus caldwellii. The staple Koorie food most commonly referred to by early settlers was murnong (or myrrnong; Microseris lanceolata), which was abundant around Melbourne at the time of settlement (and probably benefited from thousands of years of Koorie land-management). It was, however, favoured by sheep and cattle, and within a few years of settlement, local Koories complained of its virtual extinction around Port Phillip. Its nearest natural occurrence to Melbourne nowadays is probably over 30 km from the city. Fleshy fruits were eaten in season, and around Melbourne the principal fruit-bearers were probably prickly currant (Coprosma quadrifida), cherry ballart, native bramble (Rubus parvifolius), coast beard-heath, cranberry heath (Astroloma humifusum) and kangaroo apples (Solanum species). Gum or sap (mostly from black wattle) was also consumed.
After European settlement, drooping she-oak, lightwood, blackwood and yellow box were almost eliminated from the environs of early Melbourne because they were such excellent firewood. River red gum was used for fencing and building. Bark from black wattle was also used extensively in the early tanning industry. However, it was clearing - followed by agricultural, residential and industrial development - that had the greatest impact on the flora of Melbourne. Except for reserves such as Yarra Bend National Park and Cheltenham Park, much of the ground flora and understorey components of the major plant communities in greater Melbourne have been totally eliminated through clearing and/or invasion by exotic grasses and other weeds (for example, Ehrharta erecta, Sporobolus africanus, Cynodon dactylon, Oxalis species). A few tenacious native species, such as spear-grasses (Austrostipa species), wallaby-grasses (Austrodanthonia species), mat-rushes (Lomandra longifolia and Lomandra filiformis), flax-lilies (Dianella admixta and Dianella laevis) and yellow rush-lily (Tricoryne elatior), persist in a few rail reserves and 'neglected' areas, and give some indication of the more ubiquitous native species. These species are commonly referred to in early accounts of the vegetation. In most areas, only scattered remnant overstorey trees remain, and these are highly vulnerable. For example, the City of Boroondara had hundreds of yellow box trees as late as the 1970s, and many on private properties have been cut down. As early as 1939, Thomas Stephan Hart ('The Yellow Box and a lost vegetation', Victorian Naturalist, vol. 56) expressed concern about the loss of plant communities associated with yellow box in Melbourne's environs.
Wetlands in greater Melbourne have been greatly depleted because of draining and filling. Virtually none of the saline marshes of the lower Yarra remain. The most important wetlands remaining in greater Melbourne include the saline Truganina Wetlands in Altona, salt marsh near the mouth of Kororoit Creek, the Banyule and Chelsea-Edithvale wetlands - dominated by common reed (Phragmites australis), sedges (Bolboschoenus, Eleocharis) and rushes (Juncus species) - and these are threatened by weed invasion and nutrient enrichment.
One of the most dramatic changes to the vegetation of greater Melbourne in the mid-19th century was the almost complete loss of the tree form of silver banksia. Surveys from the 1840s show that it was a common plant from Altona to Essendon in the west and from Collingwood to Templestowe in the east. Since the indigenous people practised regular burning of the vegetation to exploit food plants and animals, hot wildfires were likely to have been less frequent and less intense before white settlement. The bushfires of February 1851 and subsequent grazing probably eliminated silver banksia from the region.
Preservation and enhancement of remnant plant communities is an important issue for the natural environment of greater Melbourne, and many community-based groups are involved in revegetation projects. The smaller the remnant plant community, the greater the pressure from human activities and weed invasion. Vegetation corridors are vital to ensure movement of wildlife such as birds, which contribute to pollination and seed set, and reduce insect pests. All over greater Melbourne, stately river red gums are declining from altered drainage patterns and frequent defoliation from insects and possums. If they are not managed carefully, these last witnesses of Melbourne's inexorable expansion will disappear as silver banksias and drooping she-oaks did in the 19th century.