Tuesday, 27 May 2014

Elaeagnus's sweet perfume overwhelms starry scales



The first thing you notice is the sweet perfume, then the almost oak- or olive-like leaves, then the tiny white flowers and then, and only then, the rusty or white spots all over the leaves, stems and flowers. These spots turn out to be the most interesting part of the plant, to me.


So what are we talking about? A plant commonly called Oleaster, meaning it looks a bit like an olive tree. Botanically it's called Elaeagnus, and probably Elaeagnus macrophylla from Japan and Korea (or perhaps its hybrid with Elaeagnus pungens, called Elaeagnus ebbingei). This is the specimen I saw, and photographed, at Ripponlea in April.


Elaeagnus is one of three genera in the Elaeagnaceae, a family that used to be considered a close relative of our very own Proteaceae but is nowadays of uncertain placement in the plant tree of life, somewhere near buckthorns, elms, nettles and mulberries.

Elaeagnaceae is a family of three genera and about 50 species, with only one, Elaeagnus triflora, occurring naturally in Australia (in Queensland, and extending into tropical Asia). The common name for anything in this genus is Sliverberry or Oleaster, with Elaeagnus pungens  more often called Silverthorn due to its sometimes spiny younger growth.

In southern USA (e.g. Florida), Silverthorn is invasive in native forests, even climbing trees in the most favourable areas. In the Royal Botanic Gardens we have a large - very large - clump of what we call Elaeagnus pungens but looking more like Elaeagnus macrophylla (or perhaps a hybrid; it has large, very rusty undersided leaves with a more rounded tip) growing near the Tecoma Pavilion (filling in the left of this next picture). I could imagine this taking over a forest or clambering up a tree.


So far the species don't seem to be weedy in Australia but it would be worth taking care, particularly in gardens near native bushland. Birds love the fruit, to the extent that nearly 300 were killed in one month, over 100 in one day, trying to get fruits from bushes on a Texan roadside. The rusty, spotty, red fruit of the Silverthorn at least are apparently tasty to humans as well, and it sounds like most species have edible fruits.


Now to the rusty spots and dandruff-like white flecks. Above is a close up on the top and bottom surfaces of a leaf (just to confuse things a little, the top from Ripponlea, the bottom from near the Tecoma Pavillion at Melbourne's Royal Botanic Gardens). Both I could call stellate scales, or hairs - the brown ones a little flatter on the leaf. They have radiating 'arms' so they are what we call star-shaped or stellate, and because they are rather flat and flaky the word scale seems more appropriate than hair.

This indumentum, a lovely word, might also be described as peltate (scales), because although ragged they might be viewed as a flat disk with a stalk in the middle. The density of hairs/scales and their shape and form were variable across the individuals I looked at (which may belong to two or more species or hybrids), and a study on another Elaeagnus species showed strong environmental influence on such things.

In any case, pretty little things and not dots as they appear on first glance. I assumed they might be oil glands or something of that nature. Although the surface is pocked and blemished in various ways I think most of the obvious 'dots' are these stellate scales.

So attracted by the sweet perfume then on closer inspection, almost starry skies.

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