Alders at Leybourne

I had another look at the Alder trees this Saturday and Sunday, looking at where the trees were on Saturday and trying to be sure of the ID features, and doing rather more on leafminers and other insects on the Sunday!

Italian Alder, Alnus cordata, is present as 3 - 4 trees on the short straight Eastern boundary, and another couple of trees on the southern edge near the houses, and another actually in the hedgeline. Rarely self-sown according to Pfaf, so perhaps planted, and (just to note) the seed requires 6 week stratification.

The leaf edges are heavily damaged by typical weevil feeding notches, of an unknown species. There was a Longhorn Caddis on one of the leaves, Mystacides longicornis, identified by Chris Brooks, after I failed to see it wasn't a moth, and posted it on i-spot! Also on the leaf can be seen the white specks of what appear to be leafhopper feeding marks, as well as what look like salt secretions.

A little further on there was a large mine which looked rather like Agromyzus alnivora, which does occur on this species. It gradually increases in width, and I think I could be persuaded that it had contained, at least at some stage, a double line of frass! So, it should be a Dipteran mine, and the only Dipteran known on Italian Alder is indeed Agromyza alnivora!

Grey Alder, Alnus incana, (L.) Moench

A few large trees on the south and east sides, with young trees underneath them. The young trees under the canopy of the older ones could well be root suckers!

Going back on the Sunday I noticed another Grey Alder, planted in the first formal hedgeline. I have walked past it a dozen times without even noticing it! A fine young tree, possibly a cultivar of the species. On the side-shoot I took for confirmation there was a whitish Phyllonorycter-type mine, similar in all respects, except in lacking a brownish colour, to Phyllonorycter strigulatella, the Grey Alder midget. That is a rare leaf-mining moth, distinctly local, and perhaps still nationally  notable. although I found it difficult to assign this one mine to any other species, perhaps it is safer to leave the ID as simply Phyllonorycter sp.

The mine was about 12 mm in length on a young still-expanding leaf, only 40 mm long.

On Sunday I think I finally concluded, from the leaf shape and shoot characteristics, that the Alder by the small pond was actually the hybrid Alnus x hybrida.

This is a possible mite gall on the hybrid Alder leaf, maybe Acalitus brevitarsus, but still to be confirmed by examining the erineum and its hairs under the microscope.

There was something feeding on this Powdery Mildew on the hybrid. Could have been a very wide range of things.

More on Salix city

I walked around the Ocean, anticlockwise, more slowly than the other day, and keeping an eye on as many trees as possible between the path and the lake.

Crack Willows

The first thing I thought was that at the southern end of the Ocean there is a lot of the Crack Willow, Salix fragilis (L.), the majority of the trees on the skyline. Mixed in were Ash, Grey Willow, Alders, Hawthorn, Blackthorn. The upperside of the Crack Willow leaves at this time of year are mid-green and quite glossy, with a whitish grey on the underside. The tip is quite acuminate, while the serrations on the margin are quite prominent, and somewhat uneven. The petiole is generally over 1 cm long, the twigs glossy but of variable colour, or there may be several different types present.

Crack Willow is a complex species aggregate, both in the UK and on the continent. There are many clonal variants, generally unisexual, and most of them are likely to have originated in the catchments and other areas from human activity of one sort or another. The taxonomy is very difficult. The leaves do seem to be a bit more subject to Willow Anthracnose, in comparison to the White Willow, Rusty Willow and Osiers covered below.

I was puzzled not to see obvious glands, usually figured projecting in odd shapes from the junction of the petiole and lamina.

White Willow

Salix alba appears generally to have smaller, neater, leaves obviously glistening white as they billow in the breeze. Close up it may be difficult to see the tiny hairs, except on the edges in profile, in with the minute serrations. The stems are initially silkily pubescent as well, going yellowish as they age. No stipules visible in September, and I didn't see any glands on the petiole.

Osiers

To the south and southeast, and again to the north there are good individual plants and patches of the Common Osier, Salix viminalis, L. One plant had very narrow smaller leaves, and could perhaps have been var. angustissima, but Meikle states that almost any plant will degenerate into this state if sufficiently neglected.

The shoots are generally upright, on what to me seem quite rounded bushes. The short indumentum covering the underside of the leaves and the stems and next year's buds is very attractive. On the stems the indumentum extends about half way down the current year's growth, making the younger stem a lovely silky dull green, but as it wears away, leaving a glossy green epidermis on the older stem. Last year's growth has an matt olive-brown bark covering it. The upperside of the leaves is a dull green, hardly lustrous at all. The revolute margins and the undulations are quite obvious. The underside of the leaves are silky grey with the thousands of tiny apressed hairs, and lots of small veins curving strongly towards the tip, which project downwards below the lamina, so leaving a tiny dip on the upperside of the leaves, and repeating the pattern along the incredibly long laminas. The leaves are often tattered and damaged, perhaps by leaf beetles and/or leafhoppers.

There are, but quite difficult to spot, very long, lanceolate, almost linear stipules. The canaliculate (not very obvious in September) petioles have large boat-shaped bases covering a large proportion of the bluntish woolly catkin-buds laid down for the following year, giving the string of pearls effect noted in the Collins guide. The indumentum of the stem is pierced by orange-brown stomata, generally with a central split. 

Leybourne and Salix city

Its all very difficult when you want to start to get to grips with the genus Salix. At Leybourne there is plenty of scope and there may be Salix alba, Salix fragilis, Salix caprea or Salix x reichardtii, Salix cinerea, and Salix viminalis, together with a large number of variants, cultivars and hybrids. I have suddenly remembered that there is a reference collection of Salix at the Sevenoaks Wildlife Reserve!

This is a suspected Salix cinerea ssp. oleifolia, but it will need checking and re-checking! I noticed one strium on the small section of last year's wood I remembered to collect.