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An erect shrub to 3 m tall, usually with a narrow erect spread.
It is widespread in coastal sandstone soils and lateritic and other rocky outcrops, in sclerophyll heath, woodland and forest.
It is found from the Central Coast to the Central and Southern Tablelands of New South Wales; mainly growing from north of Newcastle and around Gulgong to Ulladulla (as far west as Braidwood). Also occurs in Agnes Banks Reserve west of Sydney. There are a few largely disjunct historic records between Coffs Harbour and Grafton and a little further north and west, as well as one record on Stradbroke Island in Queensland. There are also records west of Batemans Bay further south of the main distribution in NSW.
Petrophile spp. have a somewhat complicated leaf structure. Leaves are simple but are strongly divided into segments, usually in the upper half of the leaves with the lower half acting as a linear petiole or stalk. This can be referred to as strongly pinnatisect. Sometimes, leaf segments are ternately-divided (into groups of 3). The leaf segments are also terete (tubular). Leaves are arranged alternately.
In this species, leaves are to 10 cm long to about 5 or more cm wide, at right angles to the stem, deeply divided several times with separate divided segments and, with segments rigid, terete and prickly (which differs to other NSW species); the undivided part of the leaf (stalk) is shorter than the divided part.
Petrophile spp. have many small flowers arranged in a compressed spike or ‘head’, formed in the leaf axils and terminals, with all flowers surrounded by bracts which become more woody as the inflorescence begins to fruit. Flowers have 4 tepals in the perianth (a typical Proteaceae feature) but flowers are more symmetrical in this genus.
In this species, flowers are creamy yellow, to 14 mm long. in dense, more or less ovoid, clusters, to 35 mm long on stalks less than 10 mm long; produced over most of the year.
The fruit is technically a nut (which differs to a lot of other genera). The nuts are formed within the resulting fruiting cluster of the inflorescence which has an elongated cone-shape and holds the nuts in the woody bracts. In this species, the nut is to 3 mm long, shorter than the bracts and with hairs often exceeding the bract.
Petrophile species were first introduced to cultivation in the 18th century, but these days are rarely seen outside specialist botanical and enthusiast’s gardens.
They are known to be cultivated and can do well in the right conditions.
This species requires a sandy, free draining soil in full sun.
They may die quickly due to strong wind or poor drainage due to heavy rain. But well worth growing.
Pruning after flowering is recommended.
They can be grown from seed which germinates well if fresh, although germination times may be variable from the same batch and so seed trays should be kept for some time before being discarded. Germination in some species is improved by smoke treatment, but experimental work is lacking in many taxa. Another thought for improving germination may be to remove the hairs on the nuts that seems to repel water, or nick the nuts to allow water to get to the seed embryo.
Propagation can be carried out from cuttings taken from semi-firm new growth, and treated in the regular way with the warning that the hairy leaved species should not be misted too much for fear of fungal disease.
This species is distinguished from other species of Petrophile by the rigid and prickly leaf-segments and the leaves coming off the stem at mostly 90° angles, along with a short undivided part of the leaf as well as the short inflorescence stalk (peduncle).
Petrophile is a genus of approximately 63 species with the greatest diversity being in the south of Western Australia. They also occur in Queensland, NSW and South Australia. NSW currently recognises 4 species.
Petrophile spp. will generally generate from seed after fire. This species can be seen in vast quantities in sandstone areas after fire.
Petrophile – from the Greek words petra (πέτρα) = “stone” or “rock” and philia (ϕιλία) meaning “loving” or “preferring” – referring to many species being found on rocky-habitats.
sessilis – from Latin meaning “without a stalk” (sessile), referring to the peduncle of the inflorescence.
The Australian Native Plants Society (Australia) fact sheet for Isopogon and Petrophile: https://anpsa.org.au/APOL29/mar03-3.html
NSW Flora Online (PlantNET) – Petrophile sessilis profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Petrophile~sessilis
Wikipedia profile page for Petrophile sessilis https://en.wikipedia.org/wiki/Petrophile_sessilis
Plants of South Eastern New South Wales – Lucidcentral/Online Identification app – Petrophile sessilis profile page https://apps.lucidcentral.org/plants_se_nsw/text/entities/petrophile_sessilis.htm
Fairley, A. Wildflowers of Sydney and Adjoining Areas. Blooming Books 2001, p219.