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Tom Christian (2021)
Christian, T. (2021), 'Abies durangensis' from the website Trees and Shrubs Online (treesandshrubsonline.
Tree 30–40 m, 1–1.5 m dbh. Crown of young trees narrowly pyramidal, becoming round-topped and conical-columnar with age. Bark initially smooth, greenish- or brownish-grey, lenticillate, later reddish brown and fissuring; becoming darker in older trees, breaking into irregular thick ridges and plates, deeply fissured in the bole. First order branches long, slender, spreading horizontally or slightly downswept, the tips slightly upcurved; second order branches spreading horizontally or weakly assurgent. Branchlets firm, slender, pale yellowish-green at first, soon dark reddish-brown, becoming brown with age, conspicuously grooved between the leaves. Vegetative buds oblong-ovoid, 4–5 mm long, dark brown with a dense covering of yellowish resin. Leaves set in two or more ranks on either side of shoot, pectinately outspreading, 2.5–3.5(–4.8) cm × 1–1.6 mm, slightly curved backward or forward, apex acuminate or obtuse, base twisted, dark to pale pruinose green above, pale with two dull stomatal bands below, upper surface without stomata or with a few broken lines, especially on coning shoots; leaves on coning shoots conspicuously downswept. Pollen cones axillary, 1(–2) cm long, yellowish, perular scales resinous, microsporophylls red. Seed cones sub-sessile, cylindrical-ovoid, apex obtuse, 5.5–10 × 3–4.5 cm, pale greenish-yellow when immature, ripening through yellowish-brown to brown; seed scales flabellate, 1.5–2 × 2–2.8 cm at midcone; bract scales included at maturity. (Farjon 2017; Debreczy & Rácz 2011; Grimshaw & Bayton 2009).
Distribution Mexico In the Sierra Madre Occidental in Chihuahua, Durango, Jalisco, and Sinaloa states
Habitat Cool and humid high mountain valleys and steep canyons at 1600–2900(–3400) m asl, locally forming pure stands but also commonly associating with Pinus cooperi, P. durangensis, and P. strobiformis. Broadleaf associates include Quercus castanea, Q. rugosa, and Prunus serotina.
USDA Hardiness Zone 7
RHS Hardiness Rating H6
Conservation status Least concern (LC)
Taxonomic note Debreczy, Rácz & Salazar described Abies neodurangensis in 1995, distinguishing it at species rank based on relatively minor differences in cone and foliage morphology, but with a very distinct phenology (seed cones ripening in late spring). It has a very restricted distribution a mere 22 km from the nearest stands of A. durangensis (Debreczy & Rácz 2011). It is probably not in cultivation.
Abies durangensis is one of several Mexican firs that shows affinities with both Section Grandis and Section Nobilis (Farjon 2017; Debreczy & Rácz 2011), which are familiar throughout our area in the guise of their northern representatives from the western USA: A. concolor and A. grandis in Section Grandis, and A. magnficia and A. procera in Section Nobilis. Although A. durangensis is quite distinct from all these species, this boundary blurring is typical of many firs indigenous in Mexico and Mesoamerica, the diversity of which is introduced in the article Abies in Mexico and Mesoamerica.
Few firs from this region are particularly frequent in collections; most are extremely rare. All known trees of A. durangensis appear traceable to a single introduction: the 1988 gathering of Hjerting and Ødum (no. 8), seed from which was broadly distributed among European collections on their return to Denmark. A second collection alluded to in New Trees – ‘seed collected at 3050 m in the Sierra Madre Occidental by an expedition from the Royal Veterinary & Agricultural University, Horsholm, Denmark’ (Grimshaw & Bayton 2009) – is almost certainly one and the same as Hjerting & Ødum 8, but inconsistent data recording and transfer has muddled this in several institutions.
Ironically, no trees persist at Hørsholm (University of Copenhagen 2020), but thriving examples are scattered through specialist collections in our area including: Herkenrode and Wespelaar in Belgium; RBG Kew, Ness, Westonbirt, the Yorkshire Arboretum, and Sir Harold Hillier Gardens in England; Mount Stuart in Scotland; and Fota in Ireland. The best in Britain are three at the Yorkshire Arboretum and Castle Howard: 13.6 × 0.25 m; 14 × 0.47 m; and 16.3 × 0.39 m in 2019 (Tree Register 2020). A tree at Kew had achieved 15 × 0.32 m by 2016 (Tree Register 2020), while the best of several at Mount Stuart has perhaps exceeded expectations in a very wet climate having achieved 11 × 0.23 m when seen in 2018 (pers. obs.). The tree at Fota, perhaps the only representative on the island of Ireland, was 14 × 0.35 m when seen in October 2019 (pers. obs.). The Yorkshire trees all grow in ‘woodsy’ conditions, suggesting that although full sun may be preferable it is far from essential, but A. durangensis is certainly sensitive to anything more than light shade, and to poorly drained soils.
Abies coahuilensis I.M. Johnst.
Differing from the type in its slightly smaller stature (trees to 30 m × <1 m dbh); darker coloured bark; darker coloured and pubescent branchlets; leaves shorter, 1.5–2.5 cm, a richer green green above, with a more prominent midrib below, more strongly pectinate and lacking stomata above on sterile shoots; leaves assurgent on coning shoots; seed cones with bract cusps just exserted (or included). (Debreczy & Rácz 2011).
RHS Hardiness Rating: H6
USDA Hardiness Zone: 7
Taxonomic note Several botanists prefer to treat this taxon as a distinct species, A. coahuilensis. The disparate distributions in the Sierras Madre Occidental (A. durangensis) and Oriental (var. coahuilensis) go some way to supporting this, in addition to the rather striking morphological differences. Bisbee (2018) notes that very few floristic connections exist between their two ranges.
Only a single tree of this taxon was reported in New Trees, growing at Benmore Botanic Garden in Argyll, Scotland (Grimshaw & Bayton 2009). The Tree Register now lists several other examples including: two trees at Thenford House, Northamptonshire, of 17 m × 64 cm dbh and 16.5 m × 51 cm dbh in 2019; and one at RHS Rosemoor, Devon, 5 m × 9 cm dbh in 2017 (Tree Register 2021). All these, together with another growing at Wespelaar (Arboretum Wespelaar 2021), are traceable to the same introduction, of seed gathered in Coahuila in 1987 on behalf of American seed merchant Frank Callahan and introduced to Europe by Arboretum Waasland in Belgium.
The recent discovery of several new locations for this taxon, in the Sierra Madre Oriental of Nuevo León, extends its known range and may have implications for cultivated material (Bisbee 2018). See ‘Abies vejarii subsp. mexicana’ for further discussion.