One of the tree families that suffered the most from the effects of Quaternary glaciations on the European continent is, without a doubt, that of the Juglandacea. Although one species - the walnut - managed to survive in the southern peninsulas and another - the one we are dealing with in this article - is only present in the Caucasus, on the periphery of the continent. This family had a rich diversity of species before the ice ages with genera such as Juglans, Carya, Pterocarya, Engelhardia, Platycarya, Cyclocarya, etc. Many of these genera only survived later in the Asian SE and in North America, disappearing completely from the European continent. The most thermophilic species disappeared (at the end of the Pliocene), with only the two currently present genera (Juglans, Pterocarya) and the Carya genus remaining in our continent, which survived in the Iberian Peninsula until the middle Pleistocene and until much more recent dates still in Anatolia.
The Caucasian pterocaria (Pterocarya fraxinifolia) is a species present in the W of the Black Sea, the Caucasus and the N of Iran, with some dispersed and isolated populations in Anatolia and other southernmost points of Iran. It is a thermophilic species with high demands on humidity, riparian forests being its natural habitat. As you can see on the map below, the Caucasian pterocaria was a widespread species throughout the European continent at the beginning of the Quaternary (Lower Pleistocene). It was also very abundant, being in many places the dominant species in the pollen spectrum.
Although this species was considered extinct in the Iberian Peninsula since the Middle Pleistocene, the lake record of the El Cañizar lagoon, analyzed by Eduardo García-Prieto Fronce (1), has shown that this species survived in the E of the Iberian Peninsula until the last interglacial period (Eemiense), possibly until 67,000 years ago. The warming suffered by a good part of the European continent for several decades favors, today, clearly this species that has already become naturalized in some regions in which, cruel paradox of fate, is considered invasive.
| Pterocarya | Family: Juglandaceae | Order: Fagales | |
Trees deciduous, monoecious. Branchlets with chambered pith. Terminal buds oblong, naked, or with 2-4 overlapping scales. Leaves odd- or even-pinnate; leaflets 5-21(-25), margin serrate. Inflorescences lateral or terminal on old or new growth, pendulous; male and female inflorescences separate: male spike solitary, lateral on old growth or at base of new growth; female spike terminal on new growth. Male flowers with an entire bract; bracteoles 2; sepals 4; stamens 5-18, anthers glabrous or pubescent. Female flowers with a small, entire bract, adnate to ovary but nearly free at base; bracteoles 2, adnate to ovary but nearly free above bract on posterior side; sepals 4, adnate to ovary, free at apex; style short; stigmas carinal, 2-lobed, plumose. Fruiting spike elongate, pendulous. Fruit a 2-winged nutlet, 4-chambered at base. Germination epigeal. Description: Flora of China | |||
It is a relatively uncultivated species. Most of the pterocarias grown in our country belong to the eastern species (P. stenoptera) or to the hybrid of both (P. x rhederiana). According to the catalog published by the Madrid City Council, 347 specimens of this species were planted in the Madrid Río project, but I am not sure that they really correspond to this species (it will have to be verified in situ). Its cultivation does not seem to involve many difficulties. The region from which it originates has a sub-Mediterranean type climate very similar to ours and if the water requirements of this species are met, it should thrive without much difficulty. Its propagation by seeds does not seem too problematic. Without any previous treatment (except to preserve the seeds on the terrace), I managed to germinate three seeds and I have high hopes of achieving the development of the obtained specimens..
 |
(1) Eduardo García-Prieto Fronce (2015) / Dinámica Paleoambiental durante los últimos 135.000 años en el Alto Jiloca: el registro lacustre de El Cañizar / Tésis Doctoral, Universidad de Zaragoza |
Author: Adrián Rodríguez
Translation: João Ferro
