Spanish botanist Antonio José Cavanilles described B. oblongifolia in 1800, though it was known as Banksia aspleniifolia in New South Wales for many years.

However, the latter name, originally coined by Richard Anthony Salisbury, proved invalid, and Banksia oblongifolia has been universally adopted as the correct scientific name since 1981.

[3] The bare swollen spike, now known as an infructescence, is patterned with short spiky persistent bracts on its surface where follicles have not developed.

[3] Banksia oblongifolia can be distinguished from B. robur, which it often co-occurs with, by its smaller leaves and bare fruiting spikes.

B. plagiocarpa has longer leaves with more coarsely serrated margins, and its flower spikes are blue-grey in bud, and later bear wedge-shaped follicles.

[3] In the Sydney Basin, B. paludosa also bears a superficial resemblance to B. oblongifolia, but its leaves are more prominently spathulate (spoon-shaped) and tend to point up rather than down.

[10] Derived from the Latin words oblongus "oblong", and folium "leaf", the species name refers to the shape of the leaves.

[11] Richard Anthony Salisbury had published the name Banksia aspleniifolia in 1796 based on leaves of cultivated material.

Meissner divided Brown's Banksia verae, which had been renamed Eubanksia by Stephan Endlicher in 1847,[13] into four series based on leaf properties.

Botanist and banksia authority Alex George ruled that oblongifolia was the correct name in his 1981 revision of the genus.

[3] The current taxonomic arrangement of the genus Banksia is based on botanist Alex George's 1999 monograph for the Flora of Australia book series.

In a morphological cladistic analysis published in 1994, Kevin Thiele placed it in the newly described subseries Acclives along with B. plagiocarpa, B. robur and B. dentata within the series Salicinae.

[20] George noted that Banksia oblongifolia showed considerable variation in habit, and in 1987 Conran and Clifford separated the taxon into two subspecies.

[21] New South Wales botanists Joseph Maiden and Julius Henry Camfield had collected this taller form of B. oblongifolia in Kogarah in 1898, and given it the name Banksia latifolia variety minor—B.

Field workers for The Banksia Atlas recorded 20 populations between Wollongong and Pialba in central Queensland.

[4] Locales include Calga north of Sydney, Ku-ring-gai Chase National Park, and Cordeaux Dam near Wollongong.

[4] There are isolated populations offshore on Fraser Island,[3] and inland at Blackdown Tableland National Park and Crows Nest in Queensland, and also inland incursions at the base of the Glasshouse Mountains in southern Queensland, at Grafton in northern New South Wales, and Bilpin and Lawson in the Blue Mountains west of Sydney.

[4] B. oblongifolia grows in a range of habitats—in damp areas with poor drainage, along the edges of swamps and flats, as well as wallum shrubland,[3] or coastal plateaux.

[3][6] Associated species in the Sydney region include heathland species such as heath banksia (Banksia ericifolia), coral heath (Epacris microphylla) and mountain devil (Lambertia formosa), and tick bush (Kunzea ambigua) and prickly-leaved paperbark (Melaleuca nodosa) in taller scrub, and under trees such as scribbly gum (Eucalyptus sclerophylla) and narrow-leaved apple (Angophora bakeri) in woodland.

[6] The Agnes Banks Woodland in western Sydney has been recognised by the New South Wales Government as an Endangered Ecological Community.

Here, B. oblongifolia is an understory plant in low open woodland, with scribbly gum, narrow-leaved apple and old man banksia (B. serrata) as canopy trees, and wallum banksia (B. aemula), variable smoke-bush (Conospermum taxifolium), wedding bush (Ricinocarpos pinifolius), showy parrot-pea (Dillwynia sericea) and nodding geebung (Persoonia nutans) as other understory species.

One field study in Ku-ring-gai Chase National Park found 10% opened in the absence of bushfire, and that seeds germinated, and young plants do grow.

[6] Like most other proteaceae, B. oblongifolia has proteoid roots—roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter.

[32] Not commonly cultivated,[33] it adapts readily to garden conditions and tolerates most soils in part-shade or full sun.