In identifying a plant one is often making a guess. An educated guess is still a guess and sometimes there is no correct answer. Many of the banksias belong to groups known as complexes. Members of the complex are seen as separate species but they can also hybridise – meaning that they may have intermediate forms. Any one plant may have a variety of different features, sometimes typical, sometimes weirdly different. Sometimes the scientific name serves to obscure the identity of a plant, take Banksia oblogifolia, it is supposed to have oblong shaped leaves, where the tip is blunt and the base of the leaf is relatively broad. As it happens the leaf shape is variable, and the most reliable identifying feature is a rusty coloured felt that covers the midrib and young branches. The scientific name may endure even if it is misleading because the history of the name is seen as important. The type specimens of banksia oblongifolia may have had particularly oblong leaves, but specimens from further afield may not fit in the box.
Reminds me of a job interview I did when I was fresh out of uni and looking at a temporary position to fill for a forensic botanist on maternity leave out at Lidcombe. One of the main questions they confronted me with were several marijuana leaves which did not conform to type in regards to serrated leaves, number of lobes, etc. and if I were at court how I would convince a court that the leaves were still marijuana despite these differences. Perhaps if I were as eloquent as yourself (or knowledgeable since I was definitely stretching applying as a chemist with only 6 months of horticultural studies under my belt!) I might have got the job!
Hilarious. Marijauna is easily identified by smoking (I believe)