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Grevillea caleyi, also known as Caley's grevillea, is a critically endangered species of flowering plant in the family Proteaceae, and is endemic to a restricted area around the Terrey Hills and Belrose area in New South Wales. It is an open, spreading shrub, growing up to tall with deeply divided leaves with linear lobes, and fawn flowers with a maroon to red style.
The flowers are arranged in toothbrush-like groups on a rachis long. The perianth is fawn with a villous outside. The Gynoecium is long with a maroon-red style and a green Pollen-presenter at the tip. The pistil is long and the style is . Flowering is sporadic and occurs throughout the year, mostly from August to December. Fruit is a woolly hairy follicle long with reddish brown stripes or blotches. A single, woody ellipsoidal seed long and wide is contained inside each follicle.
It is a distinctive and easily recognisable species, most closely related to G. aspleniifolia.
Species commonly associated with G. caleyi include the trees Corymbia gummifera, Eucalyptus sieberi, Eucalyptus haemastoma, Banksia serrata and Xylomelum pyriforme, the shrubs Acacia myrtifolia, Banksia spinulosa, Conospermum longifolium, Grevillea buxifolia, Hakea dactyloides, Lambertia formosa, Pimelea linifolia and Telopea speciosissima and herbaceous plants including Anisopogon, Dampiera stricta, Lomandra glauca, Lomandra obliqua and Pteridium esculentum.
Due to fecundity being low (only approximately 3% of flowers resulting in seed), seed dispersal being low and seed predation being high, it is estimated that it takes 8-12 years for a sufficient seedbank to develop to be able to replace a population. Generally, seedlings are not able to produce flowers or seeds before 2-5 years of age.
This species is pollinated by birds. Through casual observations, the likely common pollinators for this species include honeyeaters such as New Holland, white-eared and white cheeked, Silvereye, Little wattlebirds and Eastern spinebills. It is thought this species may be self-compatible as well.9780731369072, Department of Environment and Conservation. . ISBN 9780731369072
One of the greatest threats to this species is habitat loss through residential and commercial development. Approximately 85% of this species' suitable habitat has been cleared, with much of it occurring in the 20th century. Additional clearing for the widening of Mona Vale Road is resulting in further loss of habitat and is likely to result in the loss of more G. caleyi plants. The current population is severely fragmented and its population and quality of its habitat is are in continuous decline, with current population estimates suggesting the number of mature individual plants may be as low as 500-1000. An assessment published by the IUCN in 2020 estimated the current extent of occurrence (EOO) of this species to be 37 km2 and the area of occupancy at 8 km2.
It became Local extinction in one area in 2011 and a quantitive analysis by the Threatened Species Scientific Committee suggests the likelihood of another local extinction is greater than 50% in the next three generations due to habitat loss in one particular area.
Inappropriate Fire regime are another significant threat to the species. Fire is believed to play an important role in the recruitment process, as mature plants are uncommon in sites which have remained unburned for 15-20 years and seedlings sprout prolifically following bushfire events. Since individual plants take 2-5 years to reach maturity and 8-12 years are required to produce a sufficient number of seeds to regenerate a population after fire events, too frequent or too infrequent wildfires pose a major threat. Fires that occur too frequently would prevent plants from reaching maturity and producing a sufficient seedbank. Many populations are at risk of being heavily impacted or lost through too frequent fires.
Other significant, known threats to this species include weed invasion, particularly by Lantana ( Lantana camara), Privet ( Ligustrum sp.), Crofton weed ( Ageratina adenophora) Blackberry ( Rubus anglocandicans), Pampas Grass (Cortaderia selloana), Cotoneaster sp. and Acacia saligna, pathogens such as Phytophthora cinnamomi, habitat disturbance through recreational activities (eg. bike trails, horse riding) and illegal rubbish dumping.
It hybridises easily with other related grevillea species, such as with G. aspleniifolia and G. longifolia, which has resulted in a large variety of hybrids and Cultivar becoming available, including several 'Poorinda' varieties such as 'Poorinda Empress' and 'Poorinda Emblem'. The cultivar Grevillea 'Ivanhoe' is said to be a hybrid between G. caleyi and G. longifolia.
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