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Introduction: Macrozamia heteromera
is a small (Section Parazamia) cycad that is endemic to New South Wales.
It has a subterranean caudex and normally has fronds with divided pinnae.
History: M. heteromera
was named
by C. Moore in 1884 after its divided pinnae (which were observed to be different
and variable). In 1998, the M. heteromera
complex was the
subject of a major revision by David Jones, which resulted in two new species
with divided pinnae,
M. glaucophylla
and M. polymorphya
, being segregated
from M. heteromera
, after being identified by Jones as separate and distinct species.
Prior to the 1998 revision of this species, cycad enthusiasts referred to
two forms of M. heteromera
the blue form and the green form.
In retrospect, the blue form covered the species we now know as M. glaucophylla
;
while the green form covered:
(1) the species we now know to be (true) M. heteromera
,
(2) the species we now know as M. polymorpha
, and
(3) the relatively large population of hybrid plants that are evident, in and around the southern parts of the Pilliga, in areas where
M. diplomera
and M. polymorpha
grow in close proximity to each other.
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Figure 1. M. heteromera
in habitat.
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Figure 2. M. heteromera
frond.
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Distribution Range: This species has a fairly widespread distribution range in north-western New South Wales and grows in and around the Warrumbungle Ranges, to the west of Coonabarabran.
Habitat Conditions: M. heteromera
generally grows under a eucalypt canopy on undulating foothills, or stony hillsides, in the Warrumbungle Ranges. It usually grows in a pattern of more-or-less scattered individual plants, though, occasionally, it forms isolated, more populous, localised stands. This species does not tend to form large dense stands.
Climatic Data: 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.
Rainfall Patterns: 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%.
Principal Characteristics: The principal characteristics of M. heteromera
are:
- a normally unbranched subterranean caudex
- creamy-yellow callouses at the point where the pinnae join the rachis
- pinnae that are normally divided into narrow sub-leaflets
- pinnae which rise from the rachis to form a V-shaped profile
- fronds which reach a maximum length of approximately 90 cm
- light green coloured fronds
- seeds with reddish coloured flesh.
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Figure 3. M. heteromera
in habitat.
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Fronds: The number of fronds per plant varies up to a maximum of 8-10 fronds, with a norm in the 4-6 range.
New fronds generally rise from the caudex in a more or less erect stance, with the apical section tending to curve slightly. Occasionally the apical section is recurved.
Pinnae: M. heteromera
generally has fronds with narrow divided pinnae, with a typical simple division into 2 sub-leaflets.
It is not uncommon, however, to see pinnae that birfurcate very close to the rachis and split into two arms, which can both divide to form 4 sub-leaflets.
Alternatively, one of the arms can remain entire (thus forming 3 sub-leaflets) or, very rarely, both arms can divide, with one of the divided sub-leaflets again dividing to form 5 sub-leaflets.
Sometimes towards the tip of the rachis, the last few pinnae remain entire.
The pinnae on M. heteromera
are angled forward and generally rise in a V shape from the rhachis; though the lower pinnae tend to sweep sharply forward at an acute angle to the rachis, with the balance of the pinnae generally extending from the rachis in a reasonably symmetrical manner, though the sub-leaflets do overlap each other.
Cones: Coning occurs on a very irregular basis, like most inland Macrozamia species.
Female plants usually have solitary cones, though plants with 2 cones are not uncommon; while male plants can have up to 4 cones.
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Figure 4. M. heteromera
in habitat.
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Figure 5. Clump of M. heteromera
in habitat.
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Comment: M. heteromera
, incidentally, is not the species associated by some writers with the mass poisoning of sheep in the Coonabarabran district in 1929. The species involved is, without any doubt, M. diplomera
. Confirmation of this comment can be obtained by reference to a veterinary report (about the actual poisoning episode) that appeared in the June 1930 Agricultural Gazette of New South Wales and which carried a photograph of one of the offending plants.
Affinities: On an affinity basis, in respect of New South Wales cycads, M. heteromera
is related to both
M. stenomera
and
M. glaucophylla
.
Because of its multi-divided pinnae, M. stenomera
is, however, easily distinguishable from
M. heteromera
.
Likewise, because of its larger size, its bushy fronds and its glaucous blue colour,
M. glaucophylla
is readily distinguishable from M. heteromera
.
M. heteromera
has a more distant relationship to M. polymorpha
. These species are similar in size and number of fronds, but M. heteromera
normally has divided pinnae whereas M. polymorpha
generally has entire pinnae.
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Figure 6. M. heteromera
in habitat.
Figure 7. M. heteromera
in habitat.
Figure 8. M. heteromera
pinnae with 4 and 5 sub-leaflets, respectively.
Figure 9. M. heteromera
pinnae with 2 and 3 sub-leaflets, respectively.
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Contributed by:
| Craig Thompson and Paul Kennedy (Text & Figures1-9)
| | Note: This article is a revised version of a previous article by
Paul Kennedy about Macrozamia heteromera
that was published in Vol. 59 of Principes minor in November 1992,
prior to the 1998 revision of the
M. heteromera
complex by David Jones.
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