Black Locust Tree, Robinia pseudo-acacia, Cobtree Manor Park

The False Acacia or Black Locust, Robinia pseudo-acacia, (L.) is a fascinating and common tree much planted both in the United States (it comes from the Southeastern states, in particular the Appalachian and Ozark mountains), in Europe, and other parts of the world. There is a Black Locust among the five "Old Lions" of Kew. In China it is called the "Foreign Scholar Tree". It is generally regarded as a very elegant landscape tree indeed. Robinia is a genus currently restricted to North America, but traces of it do occur in Europe from Eocene and Miocene rocks. It is sometimes referred to as the tree on which America was built. When the first European settlers arrived they found it already planted where the local inhabitants lived, the various peoples having planted it from the mountains of the interior, as it was used by them in a variety of ways, including bow-making. The settlers used it extensively for building and many other uses.

It is one of the genera that does form nitrogen-fixing nodules on its roots - and it is often used in mine-spoil reclamation. The young trees grow well and vigorously, but in the U.S. they are then often infected by locust borers, at least beyond its home range, which greatly reduces its potential as a timber tree. Overseas it shows quite interesting potential. The wood if harvested young is excellent for firewood. The timber is also tough, extremely hard and rot-resistant, due to flavenoids in the heartwood. Abraham Lincoln is said to have been among the many who have produced thousands of posts and split-rail fences from this tree.

The leaves and bark are toxic, but the seeds and young pods may be edible, cooked or perhaps uncooked. The tree is often used for honey production, which is reputedly delicious, but there is often an unreliable supply, year by year. The species is unsuitable for small gardens  (Philip Hurling take note!) due to its large size, rapid growth and tendency to throw up root suckers, but the cultivar ‘Frisia’, a selection with bright yellow-green leaves throughout the summer, is occasionally planted as an ornamental tree. At the moment it appears to be suffering from a widespread but unexplained disease.

The genus is named after M. Jean Robin, and his son Vespasian, French royal gardeners of the 16th century. It was much planted in England in part due to the importation of seed from the States by William Cobbett (of Rural Rides) in the early 19th Century. It has also been said, incorrectly, that the Americans won the war of 1812 - 1815 against the British because their ships were held together with locust nails, while the British ships were held together with oak nails, and the American ships therefore survived cannonball impact so much better, that after the war the Americans made a great trade in selling locust nails to the British Navy, which insisted on them from 1813 onwards. Although this may have been partly used as an excuse for bad leadership, the locust nails did swell very effectively when wet, making their fixings fully waterproof!

The racemes of flowers which appear at the start of summer are said to smell of orange blossoms, and are edible. The colour may be whitish, pink or even apparently purple. The leaflets are said to fold together at night or when it rains - but I have never seen this! The mature shoots may carry thornless leaves, others have small paired stipular thorns of 1-2 mm. long, while the vigorous young shoots may have their stipular thorns of up to 2 cm. long.

The leaves are pinnate, 10 - 25 cm. long with 9 - 19 oval leaflets, blue-green in colour. Each leaflet may have a blunt or indented tip, with an absolutely tiny, soft spine at the very apex, only just visible. You can see the dark red colour of the young shoots behind and to the leaf, not always easy to pick out! These features tend to separate this tree from the honey locust, which has vicious spines, including often large clusters on the trunk!

The leaves are slender and hairy, with swollen bases (covering the buds of the next year's growth) - these can be seen in the pictures below.

The thorns on either side of one of the swollen stipule bases can just be seen here.

The pods are 5 - 10 cm long and dark brown, containing 4 - 10 seeds.

The bark is stated on Wikipedia to be dark grey-brown, tinged with red, deeply furrowed, with the surface inclined to scale. This particular tree is quite small and appears relatively young. The orange-red here appears mainly at the bottom of the furrows.

I have seen other photos on the internet that demonstrate a craggier bark, perhaps on older trees.

Pagoda Tree, Styphnolobium japonica, Cobtree Manor Park

There are three large Japanese Pagoda, also known as Chinese Scholar trees just beyond the Caucasian Wingnut, and maybe another, much smaller, 'Pendula' further up the slope, again with green shoots. Styphnolobium japonicum or Sophora japonica is actually from China. The species of the new genus Styphnolobium differ from Sophora in lacking the ability to form symbiotic nodules with rhizobia (nitrogen fixing bacteria) on their roots.

The buds are almost entirely hidden within the leaf-bases.

There was a historic "Chinese Scholar" Tree in Beijing, on which the last emperor of the Ming Dynasty, Chongzhen, hanged himself in 1644, at least according to some reports. There is also a record in a Chinese book published 1500 years ago, the Jin Shu, of these trees, and of poplars, planted alongside roads in cities for shade. It has also got a wide range of uses in Chinese medicine. It contains Rutin and it has been used as an abortifacient, and a dozen other uses. Although it is native to China, it is thought to have been much planted around Buddhist temples in particular in Japan, hence its better known name as Japanese Pagoda tree.

The tree can grow to a reasonable size. When grown in the open, it tends to branch quite low down, as here, but in a wood a tall straight trunk can be formed. The bark is attractively patterned to my eye "the young bark is pale gray, becoming furrowed into fibrous, interlaced, scaly ridges" (Colorado State University):

The pale creamy off-white flowers can be quite a picture in late summer/early autumn. The leaves and flowers are edible, but the pods are apparently toxic. The tree was introduced to the UK in 1753 and Kew has a tree planted in 1760, reputedly by James Gordon, a famous nurseryman, well propped up now! There is another supposedly old tree near St. Albans,  http://www.chilternsaonb.org/ccbmaps/592/137/abbey-pagoda-tree.html, which might conceivably also be a Gordon introduction.

Honey Locust, Gleditsia triacanthos, Cobtree Manor

There are three Honey Locust trees on the right at the very start of the arboretum, where the old cherries are still standing - just. The autumn colour and leaf vigour appears to differ between the trees. The thorns on the shoots are, as always, vicious and threatening, and may have been a useful deterrent against browsing by megafauna, but are apparently too widely spaced to be effective against deer. Sometimes said to have been used as nails in the past. There are also now quite a few thornless varieties that are used in landscaping and street trees. The tree is said to produce root suckers, which can be a bit of a problem, and to be be a bit pest-prone.

Here is a picture of a fairly typical bunch of trunk thorns.

This tree is found in central USA, mainly in the moist soil of river valleys. However the tree is also tolerant of poor soil conditions, and it transplants easily. It is a very serious weed in the Midwest US, and in Australia. However although its roots may fix Nitrogen somehow, there are no Rhizobium-containing nodules! One theory is that the present distribution of the tree is much smaller than its potential - perhaps because it is now missing its megafaunal pollinator partner or partners.

A related species, Water Locust (Gleditsia aquatica), grows in swamps in the southeast United States, and has similar wood properties and anatomy. There are a few other species worldwide.

The leaves are typically pinnate, but may be bipinnate on young vigorous shoots. Each leaflet looks to be finely serrate, and also has a tiny mucronate tip.

The long flat pods are sweet and edible rather than toxic, to attract some large mammalian pollinator perhaps? 

Silver Lime or Silver Pendant Lime, Cobtree Manor Park

There are three large limes in a group on the lower right of the Arboretum by the Old Cherries. They are labelled Silver lime, Tilia tomentosa, but they might be the commoner hybrid Silver Pendant Lime Tilia tomentosa 'Petiolaris'.

The petioles are generally equal to or much longer than the lengths of the leaves, and the leaves tend to hang down in consequence. The teeth looked pretty regular, and the fruit are quite globular and perhaps sulcate (BSBI crib). The tree also droops right down to the ground, which again fits the characteristics of 'Petiolaris'. The white undersides should flash in the gentlest of breezes. However I didn't see any evidence of grafting onto the stock of Common Lime, so I may be incorrect - I will have to check for grafting!

'Petiolaris' was introduced to the UK in the 1840s, planted first in the Cambridge Botanic Garden and then at Kew, and gained the RHS AGM award in 2002. It should make a graceful 30 m high domed tree, with "weeping side-branches from heavy, crooked main limbs. Leaf stalk more than half as long as leaves." (Johnson and More, the Collins Tree Guide). It is supposed to have good yellow autumn colours.

The tree is also said to be aphid-resistant but (in consequence perhaps?) the flowers are said to be narcotic to bees.  On the otherhand the instances of dead bumblebees could be exhausted bees being found around their favourite nectar plant. Anyway, here on these leaves you can see what look like Eriophyid Mite galls, with felting on the corresponding underside patches.

Here is a link to the relevant excerpt for Tilia tomentosa (Moench) from Bean's Trees and Shrubs.

Foxglove Tree, Paulownia tomentosa, Cobtree Manor Park

A lovely tree with huge leaves, and this one is fruiting very well - not bad for a tropical/sub-tropical tree from China that actually prefers climates averaging about 10C warmer than ours!

The generic name Paulownia was named by Siebold after the Grand Duchess Anna Pavlovna (or Paulowna) Romanov of Russia, who was married to King William the 2nd of the Netherlands in the early 19th Century. Apparently the axillary buds are hidden in the bark! the leaves may drop and then change colour on the ground - we shall see! This species grown here (this is by far the best known species although there may be about half a dozen recognised in and around China) is called tomentosa because of the hirsuteness of the young leaves, and, I believe of the young shoots, inflorescence and flower buds. There are three main varieties of the species, which I cannot distinguish, but which may differ in the degree of tomentosum on the leaves.

There are records of what are apparently Paulownia leaf fossils from the late Tertiary in Washington State in the USA, in the region of 5 million years ago, suggesting that this genus is another member of the Arcto-Tertiary relict fauna, now extinct over much of its likely original Northern Temperate range. These are the only known fossils relating to Scrophulariacea and its close relatives, all the other members being herbaceous and rather unlikely to be preserved in a recognisable state. This is about the time of the radiative evolution of the great apes, including the time of the first upright apes or Proto-hominoids, and the first elephants, the Mastodons, before the Ice Ages and the evolution of the Mammoths and the Stone Age. A moderately recent tree then!

The taxonomy is a little uncertain - it may be placed in the Foxglove family itself, the sole arboreal representative in the Scrophulariaceae, or in Bignoniaceae with Catalpa, or it may be placed in its own family, Paulowniaceae.

One story associated with this tree is that it was known in China as the Empress Tree, because only an Empress was allowed to have one planted on her grave - but this is maybe a little fanciful. Also from Wikipedia, also perhaps fanciful in part, "in China, the tree is planted at the birth of a girl. The fast-growing tree matures when she does. When she is eligible for marriage the tree is cut down and carved into wooden articles for her dowry. Carving the wood of Paulownia is an art form in Japan and China. In legend, it is said that the phoenix will only land on the Empress Tree and only when a good ruler is in power. Several Asian string instruments are made from P. tomentosa, including the Japanese koto and Korean gayageum zithers."

The wood is potentially very valuable and is highly valued in China (where it was harvested to near extinction) and very much in Japan, where it fits neatly into the culture. The tree is cultivated for its wood in countries such as Italy, Australia, and also in South America. It is potentially invasive, particularly it is suggested, on disturbed soils in the Eastern USA.

The seeds make the most wonderful packaging, like soft polystyrene! Used as such it may perhaps have contributed to the tree's early spread in the 19th Century in the Eastern USA. I wonder if the fruits are sticky? See the forest of dense rusty hairs on the old woody sepals here.

The bark is quite attractive, and here is a close-up of the label and bark.

It looks as though the bark makes a good substrate for lichens and algae:

The foliage and flowers are a little late to appear, the flowers being insect pollinated. The seed (about 2,000 per fruit according to one 1919 estimate) is quick to germinate, reputedly requiring light (typical ruderal), and the seedlings are quick to grow. Invasiveness might also be partly due to the tendency in some trees to throw up root suckers, occasionally in super-abundance.

Special trees of Cobtree Manor Park

As you arrive in the car park you are flanked by two Holm Oaks, and Norway Maples. There are interesting Limes, Oaks, fine Italian Alders and Sorbus in around the car park, a Broad-leaved Cockspur Thorn in the bay to the right of the main car-park, and a False Acacia by the toilets.

Before the stream on the left of the path, there are Turkish Hazels of various forms. As you cross the stream, there is a Grey Alder on your right and Honey Locusts to the right of the old Cherries. Beyond those there are Turkey Oaks and Silver Limes. Scarlet Oak? Roble and Eucalyptus niphophila by the Elephant House I think, Hybrid Tree and Willow-leaved Cotoneaster, Caucasian Wingnut, Pagoda Trees (is there a Pendula further along?), a huge Silver Maple, Swedish Whitebeam, collapsed Apple and Black Poplars on the boundary, Chestnut-leaved Oak, Foxglove tree, Golden-edged Tulip Tree, newly planted Handkerchief Trees, odd Birches. Up the top there is a newly planted Maackia and what looks like a Birch-leaved Acer.

By the pond there is Crack Willow, and more Hybrid Tree Cotoneaster, and on the other side of the path, Sweet Gum, White Willow, then going back down, Sweet Chestnuts, a group of Ash, coppiced Holm Oaks, one of Red Oaks, another of Limes, Indian Bean Tree.

By the Middle Meadow there is a Cut-leaved Hornbeam, more Limes, and on the far side there is Acer davidii, and a Wild Service Tree at the start of the Hornbeam avenue, Pears at the end?

Caucasian Wingnut, Pterocarya fraxinifolia at Mote Park

Pterocarya is an ancient genus of trees going back before the last cycle of Ice Ages, over 2.5 million years ago, at which point the Quaternary Period started, and far back into the period known as the Tertiary, 60 - 2.5 million years ago.

From fairly early in the Tertiary (The Eocene, a warm forested era with an equable climate across the whole globe, commencing with hardly any ice on the planet, when there was also the start of mammalian dominance of the megafauna) we see the members of the genus Pterocarya, and other related Pterocaryoid fossils, very widespread. At this time it is thought that there were many species in both subsections of the Juglandaceae family, and that these were found widely across Europe and North America, wherever those continents were then located (Gondwana?).

Nowadays however in the Pterocarya genus itself, there is only one extant relict species in the Caucasus, P. fraxinifolia, and around five species in East Asia, including the Chinese species, P. stenoptera. [There is only one other surviving species in the Pterocaryoid sub-family, in the genus Cyclocarya.] Prior to at least the last Ice Age, Pterocarya fraxinifolia itself was widespread across Europe, and the relatively tiny populations left in countries such as Turkey, Russia, Armenia, the Ukraine and Iran should be regarded as the lucky survivors of a once highly successful European species nearly completely wiped out by the cold and ice!

The Caucasian species of Pterocarya was apparently accidentally and unknowingly crossed with the Chinese species in an arboretum in France, and seed from that cross was exported and planted in the Arnold Arboretum in the USA in complete ignorance of its nature at  that time. All known individuals of the hybrid, P. rehderiana, appear to be derived from those original Arnold trees, and the hybrid has apparently never re-appeared!

 Several young trees of Pterocarya fraxinifolia (Poiret) Spach. have been planted around the car park - at least according to my limited ID skills! The naked buds are long small unfolded leaves, greyish and covered in thick down, but this is not so obviously rufous as in some photos on the web (taken at a different season?) - except possibly on the young shoot in close-up?

The leaflets do not to my mind obviously overlap each other. I do wonder what is meant by this. Overlapping in their pairs at the base? This feature was much more obvious and nearly universal in the lovely fruiting tree at Cobtree Manor park.

The tree is said to be a relic of the Tertiary flora that survived in or around the Caucusus. Its current distribution extends southwards to Northern Iran. The NW European Flora has it as naturalised in Southern England and Scotland as well - a result of our oceanic climate perhaps, with moist summers?

The bark of the young trees is noticeably fissured, but I didn't see overlapping ridges, at least not at this stage, as suggested in Collins:

I am not sure that these trees will do well in this situation. The tree in the Hadlow College front car park has been taken down as it has never thrived, and a new tree planted across the drive, fairly close to the main ditch. The car park seems to be a fairly dry area, and these trees are generally said to like moisture - and lots of it! The tree can be found besides rivers in Turkey, and in the relatively moist Hyrcanian Forest in Northern Iran, average annual rainfall about 1200 mm. However Hillers have them as drought-tolerant! They also sell an upright form, 'Heerenplein', which these could be I imagine - otherwise it is rather a spreading tree!

The Hyrcanian forests are themselves a relic of a more widespread, humid Tertiary dendroflora when Pterocarya was found across much of Europe. There are also several large trees by the side of the lake at Mote Park, colouring up gorgeously this week, and in my view in a much more appropriate situation!

Note the droopiness of the leaflets of this species, the only one I have seen in the UK, but as described in Collins. And these are very big multi-stemmed trees!

I came across an interesting paper by Leroy et al (2013) about the history of Pterocarya to the South of the Caspian Sea: According to them, a well-defined Pterocarya decline occurs in diagrams in Northern Iran and in western Georgia.  This takes place at ages ranging from around AD 780–1350. The decline has been variously attributed to a regional climatic drying, P. fraxinifolia being a tree of humid soils, and to human activities. Native people use the leaf of this tree as an anaesthetic agent for catching fish, for dyeing and as an antifungal agent. Its nut is edible (but pretty tiny!). Its wood however is of little use in joinery.

In the East, this decline is seen at around AD 495; therefore it occurs earlier than further west. The decline of Pterocarya in the studied region corresponds to the time when the Sasanian Empire in the early Middle Ages built the Gorgan wall and associated buildings. Human interference in the demise of  the Pterocarya therefore cannot be ruled out in addition to the aridification of the climate.

An east–west trend may also exist with an earlier decline of Pterocarya in the drier east than in the wetter west. The region of study is close to the easternmost limit of the species distribution at present. Although the pollen of this tree is abundant in the surface samples (mud and moss) of Nahar Khoran near Gorgan town, it is absent from the surface samples 190 km further east of Gorgan in the Golestan National Park. This proximity to the species distribution limits may make it more sensitive to anthropogenic or climatic changes.