Isopogon and Petrophile
Norm McCarthy
It doesn't seem right to separate Isopogon and Petrophile, two genera of Proteaceae which occur in Southern Australia, as they have so much in common. However, they will be treated individually for comparison and to avoid confusion.
Isopogon
The name is from the Greek, 'isos' - meaning equal and 'pogon' - a beard. The genus was named by Robert Brown in 1810. and currently contains some thirty-five species, twenty-seven in south-west Western Australia, while eight occur in the eastern States.
Isopogons have a wide range of leaf forms, from simple to compound, terete or flattened, which are branching and often dense. Stiff and grey/green in attractive presentation, even when not in bloom, they are eminently suited to unforgiving climates, where they excel. The inflorescence can be terminal spikes or short heads. Flowers may vary from reddish pink to mauve/purple, yellow or cream, consisting of narrow tubes that split to reveal four equal sections of intrinsic beauty.
After flowering, usually June to December, the bracts surrounding the spent floral appendage and classed as scales, fall away. The fruits form and develop into a basal nut. When ripe the multiple small black seeds, tightly packed in the hairy appendage, are dispersed as the nut disintegrates. Seed is bi-sexual and may be sown while fresh in moist compost and germinates in six to eight weeks. Damping off is not unusual if over-watered. Whilst overhead watering is not recommended, capillary watering from underneath is suggested. Reproduction from cuttings is difficult but tissue culture or grafting to a suitable rootstock could prove to be advantageous.
Isopogons favour a sandy well drained medium near coastal situations to grow well. Sandy gravel is also suitable. Plants endemic to Western Australia, where lower winter rains are usually the norm, suffer climatic inversion problems in eastern climes with higher rainfall and ensuing humidity. This is known as climatic inversion in New South Wales and Queensland. Some Western Australian plants, including Isopogon, revel in annual average rainfall of 400 to 625 mm, mostly winterwise, and a Ph level of 6 to 7. Some plants develop lignotubers for re-growth after fire.
Isopogons range from prostrate to about two metres in height. They dislike fertilisers but will tolerate slow release Osmocote at planting time. Here, I stress, it needs to be low phosphorus in content.
I am growing Isopogon dubius, I.formosus, and I.petiolaris in Toowoomba, Queensland at 700 m altitude. All are thriving and flowering in deep sand. Isopogons are commonly alluded to as "drumsticks" on the east coast of Australia. I prefer the correct given botanic term to avoid confusion. While common names may be a guide to native plants, they are not ultra specific for definitive identification.
| Photos: Australian Plants Society, Margaret Pieroni, Brian Walters |
Petrophile
Petrophile was named by Robert Brown in 1809. Ex J. Knight. The botanic name comes from the Greek 'petra', meaning rock and 'philos' - to love, and they are referred to as "conesticks" in eastern Australia, as a common name. However, this pseudonym is not used in Western Australia where the majority of species occur in nature.
These are dwarf to medium shrubs to a possible three metres, plus or minus. The genus contains forty-seven species mostly in the south-west comer of Western Australia, with one found on Kangaroo Island, while only five species are found in eastern states.
Petrophile and Isopogon grow together in harmony, and uncannily, bear a superficial resemblance to one another on near coastal sandy situations. However, some petrophiles may occur further inland in harder terrain, even in some cases 150 km from the sea. They can be found on rocky outcrops or in heavy gravel where rainfall could often be exceptionally low.
Foliage presents as quite variable with either simple, or lobed, or greatly varied lobes, usually grey/green, sometimes hairy, often flattish, dense and stiff. It is a plant of great interest even without flowers.
The inflorescence is cone shaped or global being terminal or axillary, and often profuse. Many beautiful forms exist in columns of cream, yellow, pink, mauve and grey. Floral appendages are sometimes stalked. After flowering, the scaly, often cone shaped seed vessels are produced. These fruiting cones are woody and usually sessile, sometimes stalked and often long term, remaining on the plant. The seed itself is contained as a hard nut at the base of the cone and is hairy and compressed. It takes a year for seed to ripen. Then cones may be taken from the plant and placed in a paper bag to release viable seed which germinates readily. Some petrophiles may also have lignotubers which can encourage re-growth after fire.
"Isopogons and Petrophile are closely related, having flowers that are similar in appearance ..... either in heads or shod dense spikes." (Sainsbury, R.M., 1987)
Reference
Sainsbury, R.M. (1987), A Field Guide to Isopogon and Petrophile, University of Western Australia Press.
From 'Native Plants for New South Wales', newsletter of the Australian Plants Society (NSW), July 2005.
Australian Plants online - 2006
Association of Societies for Growing Australian Plants
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