The flowers are borne in cylindrical clusters of 6 to 14 on one side of a raceme 5–15 mm (0.20–0.59 in) long.

Flowering occurs from July to October and the fruit is an oblong to elliptic follicle 12–13 mm (0.47–0.51 in) long.

[2][3][4] Grevillea thelemanniana was first formally described in 1839 by Stephan Endlicher in Novarum Stirpium Decades, from an unpublished description by Charles von Hügel.

[4][7] Spider net grevillea grows in winter-wet swampy heath in the Cannington, Kenwick and Wattle Grove suburbs of Perth, Western Australia.

[2][3] Grevillea thelemanniana is listed as "critically endangered" under the Australian Government Environment Protection and Biodiversity Conservation Act 1999 and as "Threatened" by the Western Australian Government Department of Biodiversity, Conservation and Attractions,[2] meaning that it is in danger of extinction.