It grows as an upright bush up to 2 metres (6 feet 7 inches) tall, with narrow leaves and a pale brown flower spike, which can produce profuse quantities of nectar.

The shrub grows amongst scrubland in seasonally wet lowland areas of the coastal sandplain between Badgingarra and Serpentine in Western Australia.

Arising from short lateral branchlets off stems older than four years of age, the inflorescence of B. telmatiaea is roughly oval to cylindrical, with a height of 3–5 cm (1–2 in) and diameter of 4–7 centimetres (1+1⁄2–2+3⁄4 in).

The styles are hooked rather than straight, and are initially trapped inside the upper perianth parts, but break free at anthesis.

[3] The fruiting structure is a stout woody "cone", with a hairy appearance caused by the persistence of old withered flower parts.

According to John K. Scott, "there [is] no obvious reason on the basis of morphology of pollination for this lack of seed set".

He found it most closely resembled B. leptophylla, but regarded its preference for swampy rather than sandy soils and winter flowering as worthy of warranting species status.

[2] George gave it the specific name telmatiaea from the Greek stem telmat-/τελματ- ("the mud of a pond"),[6] in reference to its swampy habitat.

[2] In 1996, Kevin Thiele and Pauline Ladiges published the results of a cladistic analysis of morphological characters of Banksia.

Leptophyllae, which Thiele defined as containing those species with "indurated and spinescent common bracts on the infructescence axes, and densely arachnose seedling stems."

[1] The placement of B. telmatiaea in George's 1999 arrangement may be summarised as follows:[1] Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae.

leptophylla B. lanata B. grossa Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subg.

[13] B. telmatiaea grows only in the Swan Coastal Plain, Geraldton Sandplains and Jarrah Forest biogeographic regions, inland from the coast but never east of the Darling Scarp.

Associated vegetation is typically scrubland or shrubland, although moisture-loving trees such as B. littoralis (swamp banksia) or Melaleuca preissiana (moonah) may also be present, sometimes in sufficient numbers to form a low open woodland.

[18] Unlike most serotinous Banksia species, the seeds of B. telmatiaea are not released immediately after the passage of a bushfire.

The introduced European honeybee (Apis mellifera) is also commonly observed, and visits by ants and Hylaeus plasterer bees have been recorded.

[21] Moreover, a number of characteristics of the B. telmatiaea spike are purported to be adaptations to pollination by nocturnal mammals: the strong, musky odour,[20] the occurrence of inflorescences hidden within the foliage close to the ground, the large amounts of nectar produced, and the pattern of nectar production, which peaks at dawn and dusk.

This last adaptation is thought to favour visits by birds and mammals, which feed in the morning and evening respectively, as opposed to insects, which are most active during the day.

On the other hand, the same study observed heavy infestation of fruiting structures, with over 90% of spikes with follicles found to contain at least one larva of an unidentified species of moth of the genus Xylorycta.

Noting that many of these cyanobacteria had heterocysts, he speculated that they aid the plant by fixing atmospheric nitrogen, which is then washed off the flower heads by rain, and absorbed by the proteoid root mat.

[23] Further investigations in 1996 suggested that the discolouration is not caused by cyanobacteria or other microorganisms in the nectar, but is rather "a chemical phenomenon of plant origin".