Macrozamia johnsonii

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Figure 1. M. johnsonii.

Contents

Introduction:

Macrozamia johnsonii is a large and spectacular cycad that is endemic to New South Wales and which, by far, is the largest of the New South Wales Macrozamia species, with a stout columnar trunk ranging up to 3 metres in height. In its various stages of development M. johnsonii can produce a normal-sized set of fronds from either a subterranean caudex, an aerial extension of the caudex or a stout columnar trunk.

History:

M. johnsonii was previously known as the New South Wales "form" or the "green" form of M. moorei, before being recognized as a separate and distinct species and segregated from M. moorei by Ken Hill and David Jones, in 1992. It was named after the late Dr L. A. S. Johnson, a contemporary botanist and former Director of the Royal Botanic Gardens Sydney, who was responsible for a major reclassification of the nomenclature of Australian cycads in 1959.

Distribution Range:

M. johnsonii has a very restricted distribution range in northern New South Wales and can be found growing on the mountain ranges between the near coastal city of Grafton and the tablelands city of Glen Innes (which is situated on the Great Dividing Range).

Habitat Conditions:

M. johnsonii normally grows under a eucalypt canopy in areas of wet, or sometimes dry, sclerophyll forest on generally steep, rocky slopes. Movement up and down these steep slopes is difficult and is exacerbated by having to contend with thick patches of Lantana vine and, also, loose rocks which have been covered over and sometimes hidden by long grass.

M. johnsonii grows prolifically in a sparsely inhabited and almost primitive area near Dalmorton, on steep hillsides which sweep down to a fast flowing river, in an idyllic, picturesque valley setting. A dirt road parallels the river for many kilometres and in some parts, where the hillsides have been cut away to make way for the road, M. johnsonii plants overlook the road in sentry-like fashion.

Figure 2. M. johnsonii

Comment:

Although M. johnsonii grows predominantly on the northern side of the river, it also grows on the hills on the southern side of the river which poses an interesting question as to whether seeds were carried across the river by animals or birds or whether the cycads grew on both sides of the valley thousands of years before the river proper was formed.

Climatic Details:

Glen Innes (elevation 1062 metres) has an annual average rainfall of 849 mms (spread over 98 rain days) with winter minimum and summer maximum temperatures (reached at least once per week during July and January) of -3.9 and 30.0°C. respectively. Frosts occur on an average of 71 days per year.

Rainfall Patterns:

Over 60% of the annual rainfall at Glen Innes falls during spring and summer. The percentage seasonal rainfall pattern is as follows: Summer 36%; Autumn 19%; Winter 19%; and Spring 26%.

Principal Characteristics:

The principal characteristics of M. johnsonii are:

  • a stout columnar trunk normally standing 0.9-1.5 metres above ground level, but sometimes reaching up to 3 metres above ground level, with a maximum trunk diameter in the 60- 80 cm range
  • mid to dark green coloured fronds which can reach up 3 metres in length
  • new fronds that initially grow, almost vertically, to full length
  • entire and sharply-tipped pinnae which are angled forward and which extend in a horizontal plane from an untwisted rachis
  • pinnae which progressively reduce in size to ultimately form spine-like appendages on the lower sections of the rachis
  • prominent whitish callouses at the point where the pinnae join the rachis
  • seeds with red coloured flesh.


Figure 3. M. johnsonii - female cones on plants at Nimbin.


Plants:

M. johnsonii can have up to 150 fronds that initially stand almost vertically, but which then, with age, tend to spread in a graceful arching manner to produce a palm-like appearance. Occasionally, M. johnsonii plants seem to retain many older dead fronds that tend to form a "skirt" (especially on trunked plants), which provides an effective contrast with the more numerous living fronds.

Cones:

Female M. johnsonii cones are the largest of any New South Wales Macrozamia species and can grow up to 65 cm in length and up to 20 cm in diameter. Female plants can have up to 6 cones, with 3 or 4 cones being common. A mature cone can weigh up to 12-14 kilograms and can contain in excess of 200 seeds. The cones are heavily spined, with an elongated spine measuring up to 6-7 cm long. These cone spines combined with sharply-pointed pinnae and the spine-like appendages on the lower sections of the rhachises make the collection of seeds from cones sitting in the crown of a plant a very hazardous occupation. Male cones, like female cones, are large and can grow to 40 cm in length and 10 cm in diameter; they are also spined, with the spines measuring up to 5 cm long. Male plants can have up to 10, or more, cones

Figure 4. Size comparison between M. fawcettii and M. johnsonii female cones.


Seeds:

Seeds of M. johnsonii are the largest of any of the New South Wales Macrozamia species and measure up to 4 cm in length and up to 2.5 cm in diameter. One unusual method which we deduced was used to facilitate the collection of M. johnsonii seeds was to cut off a number of fronds from the parent plant so as to allow easier access to the multiple cones, without being repeatedly spiked by the sharply tipped pinnae spines. The result was an odd looking, temporarily disfigured, plant with all fronds severed from an approximate 90 degree segment of the otherwise normal 360 degree spread of fronds.

General:

M. johnsonii is a quite majestic cycad, particularly when grown in cultivation. A number of large specimens can be seen growing in gardens in Grafton. In a garden in the town of Nimbin (north of Grafton), two enormous M. johnsonii plants virtually overshadow the owner"s home.

While visiting Australia in 1985, the late Cynthia Giddy, who saw cones of M. johnsonii, M. communis and a number of other Macrozamia species, commented on the lack of individuality of the various Macrozamia cones which she had seen (excluding the size of the cones on different species).

Figure 5. M. johnsonii in cultivation at Nimbin.
Figure 6. Multi-headed M. johnsonii caudex, with fronds removed,for re-location (September 2005).

Offsets:

It is extremely rare to see any offsets (or suckers) on any New South Wales Macrozamia species, though it occurs occasionally in some of the Section Parazamia species (possibly due to the plant being damaged).

In 30-odd years of looking at M. communis in the wild, we have only seen two plants with branched trunks. We have never seen a M. johnsonii plant in the wild with a divided trunk. However, an M. johnsonii plant grown from seed, in a raised garden-bed in Manly West (in suburban Brisbane), has produced a number of offsets. In September 2005, this plant was re-located to another part of the garden. The removal was made easier by using a Karcher high-pressure water gun to remove soil from the caudex and to free-up the root system. It then required 3 adult males to physically move the caudex to another spot in the garden.

Affinities:

On an affinity basis, in respect of New South Wales cycads, M. johnsonii is related to M. communis, especially those plants which grow on the far south coast of New South Wales. Young trunkless M. johnsonii plants do not look unlike mature south coast M. communis plants, though the fronds of M. johnsonii are generally longer, are a lighter shade of green than M. communis and initially stand more upright than those of M. communis.

Figure 7. Same multi-headed M. johnsonii (December 2007).
Figure 8. M. johnsonii in cultivation on a main road near Grafton.


Contributed by:

Craig Thompson and Paul Kennedy (Text & Figures 1-8)
(Note: This article is a revised version of a previous article written
by Paul Kennedy that appeared in Vol 37 of Palms & Cycads in October 1992.

External Links:

Cycad Pages, IUCN, JSTOR, Trebrown

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