Elaeo-enchanted – exploring the exquisite Elaeocarpus

Elaeocarpus stellaris DSC_0116

The glorious Elaeocarpus stellaris, a rare endemic of the wet tropics

It is well-known that the rainforest flora of the Australian tropics has a strong South East Asian element.

Various genera of laurels (Lauraceae), mahoganies (Meliaceae), tuckeroos (Sapindaceae) all appear to have origins in Southeast Asia and migrated into Australian from the north. Could there be genera of tropical rainforest trees that embody Gondwana, the memory of times when the great continents of the south were joined?

The Macadamia family (Proteaceae) might have had a good representation of a Gondwanan family, but the genera are species-poor. The genus of the lily pillies (Syzygium) is of course a prime example of a Gondwanan genus but next to this, the title of a pre-eminently Gondwanan genus goes to…Elaeocarpus!

With over twenty species, Elaeocarpus must be one of the largest Gondwanan genus in the Australian rainforest flora, and contain trees of immense cultural and ecological significance. A scientific interest in Elaeocarpus have seen a spike in the recent decades.

The director of Australian Tropical Herbarium (ATH), Prof. Darren Crayn, is a specialist in the family, and he and his students and co-researchers have published a number of papers on the family and is currently running numerous projects on Elaeocarps outside of Australia.

Elaeocarps are indeed an enchanting group of plants.

Ascertaining Elaeocarpus

A number of features in combination can be very useful in identifying the genus Elaeocarpus when no flowers are available.

1. Members of Elaeocarpus are trees

Elaeocarpus_grandis_DSC_0023

Elaeocarpus angustifolius is a fast-growing pioneer tree which can get pretty large with plank buttress roots.

2. Alternate leaves, arranged spirally around the stem

3. Leaves are often crowded at the tips of branches

Elaeocarpus bancroftii

A flowering sprig of the Kuranda Quandong (Elaeocarpus bancroftii) exemplifies the alternate, spirally-arrnaged leaves and the clustering of leaves towards branch ends

4. The outline of the leaves or the leaf margin is typically toothed

Elaeocarpus grahamii DSC_0841

The toothed margins of a leaf of Elaeocarpus grahamii, as seen from the leaf underside.

5. Stipules or stipular scars are present where the leaf stalk meets the branch.

Elaeocarpus culminicola DRO28 DSC_0769

Brown longish-triangular stipules where the leaf stalks meet the branch, here in the case of Elaeocarpus culminicola

6. Swellings on the leaf stalk where it meets both the leaf base and the twig. This is called a double pulvinus.

Elaeocarpus largiflorens DSC_0578 (7)

The leaf stalks of Elaeocarpus largiflorens are swollen at both ends where they meet the leaf and the stem

7. Leaves often wither deep red or orange

Elaeocarpus johnstonii

The leaves of Elaeocarpus johnstonii withers dark orange

8. Many species have foveoles or domatia (caverns or pits) where the nerve radiates from the midrib (best seen on the leaf underside)

Elaeocarpus coorangooloo

Structures called domatia or foveoles are often present at the junctions between the veins and the midrib, as seen in this example of Elaeocarpus coorangooloo.

Thou shalt know thy Elaeocarps when they flowers and fruit

The flowers often have frilled petals, are usually white, yellow, cream to pink, on a spike that arises from a leaf axil, and hang downwards.

Elaeocarpus coorangooloo

The fruits are usually fleshy (often bluish) with a hard, and often ornamented “stone” Some species have fruits that mature deep purple, brown or greyish blue.

Elaeocarpus angustifolius IMG_7078

The Bluish fruits of Elaeocarpus angustifolius

Elaeocarpus eumundi

In Elaeocarpus eumundi, the rough surface of the seeds is accentuated with persistent fibres

Elaeocarpus always have somewhat fleshy-gritty fruits with a stone. The stone often also reveals a rough surface when the flesh rots off.

In many tropical regions in Asia and also in Australia, the hard seeds have religious or spiritual significance, and are often used to make jewelry.

Elaeocarpus angustifolius DSC_0910

The famous Rudraksha beads used to make Indian religious jewelry come from the seeds of Elaeocarpus angustifolia.

Just to make life interesting (or confusing), many arborescent members of the Spurge family (Euphorbiaceae) have these combination of features above as well. Same goes to the family of the Malvaceae.

However, many of the Euphorbiaceae have some kind of sap or raised glands on their leaves, while Malvaceae often have three-nerved leaves, or with star-like hairs on the leaf surface

Ultimately, flowers or fruits really help with distinguishing Elaeocarpus from genera of Euphorbs and Malvaceae as the fruits of the latter two families are typically capsules which open up along suture lines.

References

Crayn, DM, M Rossetto, DJ Maynard (2006) Molecular phylogeny and dating reveals an Oligo-Miocene radiation of dry-adapted shrubs (Tremandraceae) from rainforest tree progenitors (Elaeocarpaceae) in Australia. American Journal of Botany 93: 1168-1182.

Elaeocarpus foveolatus DSC_1111

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About David Tng

I am David Tng, a hedonistic botanizer who pursues plants with a fervour. I chase the opportunity to delve into various aspects of the study of plants. I have spent untold hours staring at mosses and allied plants, taking picture of pollen, culturing orchids in clean cabinets, counting tree rings, monitoring plant flowering times, etc. I am currently engrossed in the study of plant ecology (a grand excuse to see 'anything I can). Sometimes I think of myself as a shadow taxonomist, a sentimental ecologist, and a spiritual environmentalist - but at the very root of it all, a "plant whisperer"!
This entry was posted in Edible plants, Elaeocarpaceae (Quandong family), Habitat - Rain forest, Learning Plants, Lifeform - Trees & Shrubs and tagged , , , , , , , , . Bookmark the permalink.

2 Responses to Elaeo-enchanted – exploring the exquisite Elaeocarpus

  1. Pingback: Elaeocarpus angustifolius (Elaeocarpaceae) | Leaf Whispering in the Tropics

  2. Pingback: Finding the kernel of truth | David Tng

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