Introduction: Macrozamia communis is a large (Section Macrozamia) cycad that is endemic to New South Wales. It can have either a subterranean caudex, an aerial extension of the caudex or a short columnar trunk.
History: M. communis was described and named in 1959 by the late Dr L. A. S. Johnson (a former Director of the Royal Botanic Gardens Sydney) because of its habit of growing in large communities.
Distribution Range: M. communis grows over large sections of coastal New South Wales and adjacent slopes and ridges of the Great Dividing Range. It has the most extensive distribution range of any cycad in New South Wales and is the most commonly occurring cycad in New South Wales. The distribution range extends from the Taree region (on the mid-north coast) some 600 kilometres to near Bega (on the far south coast). Sydney, where a number of large stands can be found, is located approximately half-way between Taree and Bega. The distribution range of M. communis was reduced considerably when M. montana and M. reducta were segregated from M. communis in 1998.
Figure 1. Craig Thompson (1.9 m tall) by a large trunked M. communis .
Figure 2. M. communis with skirt of dead fronds.
Habitat Conditions: M. communis grows prolifically, in some areas abundantly, on the south coast of New South Wales and to a slightly lesser degree on the central coast, north of Sydney. M. communis reaches its maximum population density on stabilised sand dunes in close proximity to the ocean. It also grows in dense stands on steep hillsides and slopes of near coastal ranges. M. communis grows in areas of woodland, open forest or tall open forest. On the south coast it grows principally under a canopy of Corymbia maculata (previously Eucalyptus maculata); where C. maculata (the spotted gum) is present, M. communis is normally the dominant understorey plant, although scattered Banksia sp are often present. On the Central coast, the principal canopy cover is provided by Angophora costata (the Sydney red gum).
As a general rule (thought this is not an ironclad rule) M. communis usually forms a subterranean caudex on coastal sand dunes (due to the action of contractile roots), whereas in shallow soils and on quartzite and sandstone ridges it tends to form an aerial extension of the caudex or a short columnar trunk. Despite the above comment, however, the old adage that the only consistent factor about cycads is their inconsistency applies to this species, as trunked specimens are common in some stands that have formed on coastal sand dunes.
Near Batemans Bay on the south coast, M. communis is ubiquitous and can be found growing in numerous dense and extensive stands. There are literally thousands upon thousands of plants growing within a 20 kilometre radius of Batemans Bay (albeit that many stands have been decimated in the name of progress to make way for homes, farms or tourist developments).
In some dense stands on the south coast of New South Wales, M. communis grows in such abundance that, in order to move through a stand, it is necessary to force your way through the overlapping fronds of numerous closely growing plants and simultaneously protect your eyes from the sharply-tipped pinnae (on fronds which can reach up to 2.4 metres above ground level, from a subterranean caudex). The density of plants in some of the above stands is such that the ground is often totally obscured by the multiple layers of fronds and it is virtually impossible to see where, or on what, you are treading as you move, with great difficulty, through the crowded plants.
No other cycad in New South Wales (or to our knowledge in Australia) has a population density of the same magnitude as M. communis . In this respect, despite the fact that we have described Lepidozamia peroffskyana as growing in abundance with adult plants growing so prolifically that the fronds of numerous plants growing very close together actually overlap each other, the population density of M. communis in certain areas on the south coast of New South Wales far exceeds the density of the most populous stands of L. peroffskyana that we have seen.
M. communis increases significantly in size as it moves southward. Not only does the overall size of the plants increase but there is a corresponding increase in the size of both cones and seeds. We have been advised by Keith Boyer, a New Zealand cycad enthusiast, that plants grown from seed collected near Batemans Bay grow much better in the temperate climate of New Zealand than plants grown from smaller seeds collected from smaller plants near Gosford (on the central coast).
Figure 3. M. communis in habitat.
Climatic Data: Climatic information relating to Taree, Sydney and Bega and covering altitude, annual average rainfall, number of rain days and frost days per year and minimum and maximum temperatures reached at least once per week in July and January, respectively, is as follows:
Place Altitude (metres) Annual Average
Rain Days Frost Days Temperature Range
July min January max Taree 8 1178 110 10 1.3 33.3 Sydney 42 1216 139 Nil 5.7 28.9 Bega 11 879 94 61 -2.5 32.3.
Figure 4. Craig Thompson examining M. communis in habitat.
Rainfall Patterns: The annual rainfall covering the overall distribution range of M. communis falls in a very uniform pattern with 50% falling in spring and summer and 50% falling in autumn and winter. The percentage seasonal rainfall pattern is as follows: Summer: 28%, Autumn: 28%, Winter 22% and Spring 22%.
Principal Characteristics: The principal characteristics of M. communis are as follows:
- plants with either a subterranean caudex, an aerial extension of the caudex or a short columnar trunk
- a normally unbranched trunk though plants do branch on an extremely rare basis (see photo; but note that some of the lower fronds on the plant were removed so as to permit a clear view of the divided trunk)
- dark green coloured fronds which become dull with age
- an untwisted rhachis
- entire and sharply-tipped pinnae which are angled forward (at an angle of 45-60 degrees to the rhachis) and which extend in a horizontal plane from the rhachis
- pinnae which progressively reduce in size and become spine-like towards the base of the rhachis
- a prominent whitish callous at the point where the pinnae join the rhachis (though plants in the Sydney suburb of Menai sometimes have pinkish callouses)
- seeds which can have red, orange or yellow coloured flesh
Figure 5. M. communis with divided trunk.
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