Acer pensylvanicum - Moosewood - the coloured bark form labelled 'Erythrocladum'

Acer davidii 'Serpentine' - and the inconsistency of text descriptions !

One of the nicest things about the small tree in the semi-shade labelled as Acer davidii 'Serpentine' just to the north of Sandell Lake in the College grounds is the fulsome display of fruits above your head and against the sky as you stand underneath the arching boughs. The fruit nutlets are green and the fruit wings yellowish to pinkish in this tree at the moment. The branches are densely leaved as well as fruited and the overall effect is somewhat ethereal.

Bluebell Nurseries proclaim a yellow autumn colour for their plants, while Ornamental Tree Nurseries say that theirs colour up a deep red, and the Shoot website and Larch Cottage Nurseries claim their trees' leaves become a deep orange. Does it vary with the plant's genetics or environment I wonder, or are the colours just variable on each tree? I wonder what this particular College tree will end up as?

There is similar variation in the described colours of the fruits (pink-brown or red) and the bark (red, purplish). The petioles may be green (in the shade?) to pinkish. A. davidii ssp davidii is partly separated from A. davidii ssp grosseri in at least some texts by the former's pink to red petioles and the latter's green ones.

Here is a quote from the TreesandShrubs online: † cv. ‘Serpentine’. – A selection raised from seed in Holland, apparently from Forrest’s form, with smaller leaves than normal. Young wood brown. (http://treesandshrubsonline.org/articles/acer/acer-davidii/).

This is quoted from the Polish PlantMar website: "This cultivar was discovered as a chance seedling in a nursery in Boskoop (Holland), raised and introduced by W.J. Hooftman in 1976. Much smaller than the type, forms small shrubby trees to 5-6 m high by 4 m. Leaves dark green, narrow and oval, almost unlobed (specially on older plants), smaller than the species (10 cm long) with red petioles. The bark is the most ornamental. On young shoots it is carmine-red to purple (specially nice in the winter) with distinctive, creamy stripes. Here is a picture from a shoot in the sun that seems to capture the colour of the petioles, the summer shoots and the one year old twigs."

Again from the PlantMar website, "the older twigs are olive-green with vertical pearl-white stripes. Buds red. Fruits abundant, samaras to 2 cm long. Autumn colours orange and yellow, not so reliable. Good plant for smaller gardens."

I wonder if the bark could be improved by cleaning off the lichens, etc? These two pictures below are of quite large main trunks, about xxx girth, so obviously refer to the older bark description above "olive green with pearl-white stripes".

One feature that every website seems to agree on however, is that the leaves of this cultivar are rather narrower than the type. This picture below seems to indicate the relatively narrow leaves of this Cultivar, as well as what might be leaf damage caused by a hungry caterpillar.

Acer davidii 'George Forrest' and 'Earnest Wilson'

This first series of photos of a cultivar of Acer davidii was seen at the Cobtree Manor Park between Aylesford and Maidstone in October. 2015. I think it is probably Acer davidii 'George Forrest'. This is still a small tree here, in its native habitat the species is a medium-sized spreading tree that can grow to 10 - 15 m.

According to Wikipedia, the leaves are 6–18 cm long and 4–9 cm broad, with a petiole 3–6 cm long; they are dark green above, paler below, ovate, unlobed or weakly three-lobed, with a serrated margin. They may turn to bright yellow, orange or red in the autumn. The flowers are small, yellow, with five sepals and petals about 4 mm long; they are produced on arching to pendulous 7–12 cm racemes in late spring, with male and female flowers on different racemes. The samara nutlets are 7–10 mm long and 4–6 mm broad, with a wing 2–3 cm long and 5 mm broad.

'George Forrest' is a cultivar of Acer davidii (subspecies davidii?) that is said to have originated in Scotland. The species was originally discovered by Pere Armand David, in 1869 and rediscovered by Charles Maries a few years later, 1878.

The species description states that samara nutlets are 7–10 mm long and 4–6 mm broad, with a wing 2–3 cm long and 5 mm broad, at nearly 180 degrees. Flowers small, yellowish, in slender, pendulous, 5-7.5 cm long, clusters (racemes); female clusters longer than male.

These particular leaves are not very serrated, toothed or lobed. Pictures on the internet appear to indicate a degree of variability! Oregon State University points out that in the species on younger plants almost all the leaves are tri-lobed, and their own plant (of the species) is nearly entirely three-lobed. One feature that appears reasonably consistent is the  crimson red of the petioles, and a variable reddishness of the shoots. The young leaves are also reddish as they unfold.

The stem is greenish with white stripes. The whitish stripes, characteristic of these snakebark maples, are said to be due to waxes that accumulate in the valleys of the bark, and may therefore be quite variable, dependant upon the ebbs and flows of the wax:

The next series of photographs is of another tree, this time in Dunorlan Park, and earlier in the season, at the beginning of August. I think this could be the cultivar 'Earnest Wilson' perhaps - they do seem quite narrow and unlobed, there does seem to be a bit of a v-fold at the base of the leaves, and they are perhaps a bit greyish underneath. so perhaps I should consider this. The arching habit is quoted on some websites. If so, there should be a good orange autumn colour, not seen in 'George Forrest', but the leaves should not unfold in the early dark orange flush characteristic of 'George Forrest'.

In this case the petioles are a light reddish-pink rather than bright scarlet, and this could perhaps be due to the time of year, or perhaps 'George Forrest' isn't the right ID, and 'Earnest Wilson' is.

It was interesting to see on these ripening samaras that the area of the nutlets remain a strong green while the wings have started to colour up quite well. I also saw this pattern in the tree labelled as Acer davidii 'Serpentine', which is encouraging if it is thought to be a feature of the species.

So interesting to compare with the samaras of the tree tentatively identified as Acer rufinerve in Dunorlan Park where this colour pattern is entirely reversed.

Here is a picture of one of the main stems, showing the "white, green and brown vertical striping" and some of the horizontal break-lines in the bark that we see in some of the on-line images, unreliable as they are. On this plant, there are none of the dark purple stripes that you see in some online photos, however.

Acer rufinerve - a snakebark maple

A single plant of Acer rufinerve, the Grey-budded, Red-veined or Honshu Maple from central Japan, is on the planting list at Dunorlan Park and I think must be the ID of the relatively broad-leaved Snakebark Maple planted in the half shade above the boathouse and the large oaks, beeches and limes on this slope.

According to the key, Acer rufinerve falls into the Macrantha group L on the key, those with 3-5 or 5 lobed leaves and membraneous pockets in the underside vein axils. This key makes no mention of the obvious reddish tufts of hairs also in the axils, which some authors say are persistent, as they appear to be here. Others claim that the hairs disappear in the summer, and the University of Copenhagen states that they are not found on the most vigorous shoots.

The overall mature leaf outline is said to always be obovate (quite broad?), as opposed to quite variable in a variety of other small Acers. The young shoot should then be blue-whitish bloomed to distinguish it from A, pensylvanicum which has a green young shoot, and usually longer obovate leaves. The petiole is greenish, as described by most books.

The plant in Dunorlan Park often look rather speckled with yellow and could perhaps be infected with a visible virus.

In July 2018 the developing fruits on this tree showed red where the seeds are, while the wings remain green. this is a feature of Her's Maple noted in the Collins Guide but Her's Maple (Macrantha Group K in the key) has its reddish hairs in the leaf axils soon lost, persistent white pegs, and stubbier side-lobes. Although it looks as though the seeds are developing well, the tree is dioecious according to Wikipedia, so the seeds will probably be infertile. This doesn't sound like an invasive species - see below? In addition, the sex of the trees is said to be malleable with environmental conditions according to researchers who worked in its native range in Japan.

The young stem is that lovely green-striped pattern that you see in the books - but the overall shape of the young tree is rather disappointing, rather too upright and ungainly I thought - and the potential space for this tree is a little cramped. so I don't think that will change. Note the greenish bud in this photo, not yet obviously white-bloomed.

Amazingly, this tree is said to show signs of invasive-ness in Belgium!

Acer griseum and other compound -leaved Acers with dark imbricate scales on their buds

There is an Acer griseum beside the driveway into Hadlow College - and it is very nearly the recorded size of the County Champion at Cherry Ingram's old house, the Grange at Benenden.

The vegetative Acer key moves into Group B, when you are looking at trees with compound leaves, and then into either trifoliate or pinnate leaves. The next important step is to look closely at the buds. If there are just two non-overlapping bud scales, then you are off towards cissifolium, henryi, and negundo. A. cissifolium has brown woody second year twigs, and trifoliate leaves with pointy leaflets, while the other two have green or purplish second year twigs. A. henryi has trifoliate leaves while A, negundo is the familiar Box Elder with pinnate leaves, normally five. I can deal with these in a separate post focussing on Acer negundo.

If there are more than four dark overlapping scales, then you are off towards mandschuricum, triflorum, griseum and maximowisczianum (nikkoense). A. mandschuricum, The Manchurian Maple, a smallish upright tree with good autumn colour, has glabrous (contrasting red) petioles with quite lanceolate slightly toothed leaflets, while the petioles of the other three are hairy-fuzzy. A. triflorum has the underside leaf pubescence largely restricted to the main veins, and the bark coarsely vertically fissured. A. griseum and maximowisczianum (nikkoense) have obvious pubescence under their leaves, with peeling orange bark on A. griseum, and smooth bark on A. mazimowisczianum. The former tends to few lobes decreasing towards the apex, while the latter has perhaps more shallower lobes or blunt teeth of equal size.

A. griseum is the commonest seen as an ornamental tree in the west, as the overall effect is quite stunning, while the other species are quite rarely planted. From a distance the leaves of A griseum are an attractive matt almost grey-green against the orange curls of the trunk and branches.

This a close up of the dark scaled (4+ imbricate scaled) buds and the pubescent petioles:

This is the underside of the leaves: