The type specimen of Banksia seminuda was collected on 15 May 1973 in Nanga Brook, Western Australia by Alex George, who described it in 1981 as a subspecies of B. littoralis.
He had published a taxonomic arrangement of Banksia in his landmark 1981 monograph The genus Banksia L.f. (
Proteaceae).

In 1984, botanist Barbara Rye of the Western Australian Herbarium noted that the two species did not interbreed when they occurred in stands together in the Two Peoples Bay region.
This was despite an overlap in their flowering seasons.
The bark of the trunk and flower structure differed greatly between the species.
B. seminuda grew alongside rivers while B. littoralis grew in wet depressions.

Endlicher's Eubanksia became B. subg.
Banksia, and was divided into three sections, one of which was Oncostylis.
Oncostylis was further divided into four series.
After its discovery, B. seminuda placed in series Spicigerae because its inflorescences are cylindrical.

In 1996, Kevin Thiele and Pauline Ladiges published a new arrangement for the genus, after cladistic analyses yielded a cladogram significantly different from George's arrangement.
With respect to B. seminuda, their findings largely accorded with George's arrangement: section Oncostylis was discarded as polyphyletic, but series Spicigerae was inferred to be monophyletic, and B. seminuda appeared as the closest relative of a clades of B. littoralis and B. verticillata:
This clade became the basis of Thiele and Ladiges' B. subser.
Occidentales, which was defined as "characterised by opposite-decussate seedling leaves and adult leaves in true whorls."
This arrangement stood until 1999, when George largely reverted to his 1981 arrangement in his monograph for the Flora of Australia series.
Under George's taxonomic arrangement of Banksia, B. seminuda's taxonomic placement may be summarised as follows:
Banksia
B. subg.
Banksia
B. sect.
Banksia (9 series, 50 species, 9 subspecies, 3 varieties)
B. sect.
Coccinea (1 species)
B. sect.
Oncostylis
B. ser.
Spicigerae (7 species, 2 subspecies, 4 varieties)
B. spinulosa (4 varieties)
B. ericifolia (2 subspecies)
B. verticillata
B. seminuda
B. littoralis
B. occidentalis
B. brownii
A 2013 molecular study by Marcel Cardillo and colleagues using chloroplast DNA and combining it with earlier results found that B. seminuda was sister to a combined lineage that gave rise to B. quercifolia and B. oreophila.
The ancestor of these three taxa had diverged almost 20 million years previously from the ancestor of the western Australian members of the Spicigerae and B. nutans.
The type specimen of Banksia seminuda was collected on 15 May 1973 in Nanga Brook, Western Australia by Alex George, who described it in 1981 as a subspecies of B. littoralis. He had published a taxonomic arrangement of Banksia in his landmark 1981 monograph The genus Banksia L.f. (Proteaceae).
In 1984, botanist Barbara Rye of the Western Australian Herbarium noted that the two species did not interbreed when they occurred in stands together in the Two Peoples Bay region. This was despite an overlap in their flowering seasons. The bark of the trunk and flower structure differed greatly between the species. B. seminuda grew alongside rivers while B. littoralis grew in wet depressions.
Endlicher's Eubanksia became B. subg. Banksia, and was divided into three sections, one of which was Oncostylis. Oncostylis was further divided into four series. After its discovery, B. seminuda placed in series Spicigerae because its inflorescences are cylindrical.
In 1996, Kevin Thiele and Pauline Ladiges published a new arrangement for the genus, after cladistic analyses yielded a cladogram significantly different from George's arrangement. With respect to B. seminuda, their findings largely accorded with George's arrangement: section Oncostylis was discarded as polyphyletic, but series Spicigerae was inferred to be monophyletic, and B. seminuda appeared as the closest relative of a clades of B. littoralis and B. verticillata:
This clade became the basis of Thiele and Ladiges' B. subser. Occidentales, which was defined as "characterised by opposite-decussate seedling leaves and adult leaves in true whorls." This arrangement stood until 1999, when George largely reverted to his 1981 arrangement in his monograph for the Flora of Australia series. Under George's taxonomic arrangement of Banksia, B. seminuda's taxonomic placement may be summarised as follows:
Banksia
B. subg. Banksia
B. sect. Banksia (9 series, 50 species, 9 subspecies, 3 varieties)
B. sect. Coccinea (1 species)
B. sect. Oncostylis
B. ser. Spicigerae (7 species, 2 subspecies, 4 varieties)
B. spinulosa (4 varieties)
B. ericifolia (2 subspecies)
B. verticillata
B. seminuda
B. littoralis
B. occidentalis
B. brownii
A 2013 molecular study by Marcel Cardillo and colleagues using chloroplast DNA and combining it with earlier results found that B. seminuda was sister to a combined lineage that gave rise to B. quercifolia and B. oreophila. The ancestor of these three taxa had diverged almost 20 million years previously from the ancestor of the western Australian members of the Spicigerae and B. nutans.
Banksia seminuda