Macrozamia polymorpha is a small (Section Parazamia) cycad that is endemic to New South Wales. It has a subterranean caudex and pinnae that can be either entire or divided.
M. polymorpha was described and named in 1998 by David Jones, when it was recognised as a separate and distinct species. It had previously been identified under the M. heteromera umbrella, and was known amongst cycad enthusiasts as the "Coonabarabran hybrid." It was named after its many forms.
M. polymorpha grows in north-western New South Wales in and around the area between Coonabarabran and Gunnedah, in a region which, in general terms, covers the southern sections of the Pilliga.
M. polymorpha grows in deep sandy soil in dry, flat country, in a pattern of scattered individual plants. It can be found growing in the Rocky Glen area, about 35 km east of Coonabarabran. It normally grows under a canopy of eucalypts and native pines.
Coonabarabran (elevation - 509 metres) has an annual average rainfall of 735 mm (spread over 80 rain days) with winter minimum and summer maximum daily temperatures, reached at least once per week during July and January, of -3.6°C and 35.9°C. respectively. Frosts occur on an average of 76 days per year.
One-third of the annual average rainfall at Coonabarabran falls in summer, with the balance of the rainfall being spread evenly (on a seasonal basis) over the rest of the year.
The seasonal rainfall pattern is as follows: Summer: 32%, Autumn: 23%, Winter: 22% and Spring: 23%.
This species is somewhat unique insofar as its fronds have pinnae that can be either predominantly entire or can have a varying combination of entire and divided pinnae, though plants with fronds having predominantly entire pinnae are more common. Pinnae variations can occur on fronds on different plants in the one stand; and, not infrequently, pinnae variations occur on the fronds of plants growing adjacent to each other.
The principal characteristics of M. polymorpha are:
- a subterranean caudex
- obliquely erect to spreading fronds, with the apical section being strongly recurved
- bright green coloured fronds
- variations in frond/pinnae characteristics on individual plants
- pinnae that extend from the rhachis in a broad V-shaped profile
- creamy-yellowish callouses where the pinnae meet the rhachis
- seeds with reddish coloured flesh.
Plants have up to a maximum of about 10 fronds, with the norm being in the 3 to 5 range. The fronds grow up to 1 metre in length.
Cones on female plants are usually solitary, though plants with 2 female cones are not uncommon. Male plants can have up to 3 cones.
Observation of cycads around the Coonabarabran, where both M. diplomera and M. polymorpha grow, clearly indicates examples of hybridisation. According to David Jones in Cycads of the World (Second Edition): "M. polymorpha hybridises with M. diplomera where the two species grow in close proximity."
Any enthusiast who has examined plants growing around the Coonabarabran area will be familiar with the problems of conclusive species identification, in and around areas where M. diplomera and M. polymorpha grow.
With its hotchpotch of forms, M. polymorpha has little in common with other species that have predominantly divided pinnae (M. diplomera, M. glaucophylla, M. heteromera and M. stenomera) other than its trait of producing plants with variable numbers of divided and entire pinnae. It is, however, more closely allied to M. heteromera than to any of the other species which predominantly divided pinnae. Even so, M. polymorpha can be readily distinguished from M. heteromera because it has broader, bright green pinnae that are predominantly entire.
Some of the local inhabitants:
Paul Kennedy and Craig Thompson (Text and Figures 1-11)