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!
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.
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