Banksia leptophylla is one of five
Banksia species, all closely related to
B. sphaerocarpa, that have highly unusual flower
nectar. Whereas other
Banksia species produce nectar that is clear and watery, the nectar of these species is pale yellow initially, but gradually becomes darker and thicker, changing to a thick, olive-green mucilage within one to two days of secretion, and eventually becoming "an almost black, gelatinous lump adhering to the base of the flowers". It was first noted by
Byron Lamont in 1980; he attributed it to
cyanobacteria that feed off the nectar
sugars. 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. This purported
symbiosis was investigated by Barrett and Lamont in 1985, but no evidence of nitrogen fixing was found. Further investigation by Markey and Lamont 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". Their analyses indicated that the nectar had unusually high levels of sugar and free amino acids, but three of these species, including
B. leptophylla, have since been shown to have normal nectar sugar compositions. An assessment of the potential
impact of climate change on
B. leptophylla found that its range is unlikely to contract and may actually grow, depending on the severity of the change and how effectively the species migrates into newly habitable areas. ==Conservation status==