It generally grows as an open woody shrub or small tree to 5 m (16 ft) high, with stiff serrated leaves and unusual hanging inflorescences.

Banksia lemanniana grows as an open shrub or, less commonly, a small tree to 5 m (16 ft) in height, with a spreading habit.

In it, Drummond states "On Mount Barren I found... a remarkable nodding yellow-flowered Banksia, with leaves and a habit so like B. Caleyii, that it can only be distinguished by the cones and flowers, which are widely different."

[7] The name Banksia lemanniana first appeared in print in 1852, being included in "A List of the Proteaceae Collected in South-Western Australia by Mr James Drummond", written by Carl Meissner and published in Hooker's Journal of Botany and Kew Garden Miscellany.

[8] Four years later, Meissner published a formal species description in his chapter on the Proteaceae for A. P. de Candolle's Prodromus Systematis Naturalis Regni Vegetabilis.

[9] Neither of Meissner's publications gives an etymology for the specific epithet, but it is now accepted as honouring the English botanist Charles Morgan Lemann.

[4][11] Meissner placed B. lemanniana in series Quercinae in his 1856 arrangement of the genus on account of its strongly dentate, cuneate to obovate leaves.

Tetragonae was found to be monophyletic, and therefore retained; and their analysis of the relationships within the series supported the placement of B. lemanniana as sister to the pair of species B. aculeata and B. caleyi.

Under George's 1999 arrangement, B. aculeata's placement was as follows:[5] Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae.

[20] Banksia lemanniana is found near the southern coast of Western Australia, most of its population protected within Fitzgerald River National Park.

Outside the park, it reaches the Ravensthorpe Range to the northeast and the rabbit-proof fence to the east, as well as isolated populations westwards as far as Pallinup estuary.

[3] It is found on the tops and slopes of hills as well as flatter areas on rocky or lateritic soil, as well as sand, in mallee scrubland or heath.

Banksia lemanniana is relatively secure as much of its range lies within a National Park, and it is not a species collected for the cut flower industry.

[21] A variety of pollinators have been recorded visiting the flower spikes, including New Holland honeyeater (Phylidonyris novaehollandiae), red wattlebird (Anthochaera carunculata), native and European honey bees, wasps and ants.

[4] The flower spikes drip nectar onto the ground or lower leaves, suggesting pollination by nonflying mammals, which are attracted to the scent.

[4] If fire occurs too frequently, plants are burned before reaching maturity or before they have produced sufficient seed to ensure regeneration of the population.

[24] A study on cultivated plants in South Australia inoculated with P. cinnamomi and P. citricola found B. lemanniana to have an overall low susceptibility overall to both organisms, although 2-to-3-week-old seedlings appeared more vulnerable than 10-month-old ones.

It favours a sunny position and good drainage, and has been successfully cultivated in more humid climates on Australia's east coast.