Alnus hirsuta (Spach) Rupr.

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Credits

Tim Baxter & Hugh A. McAllister (2024)

Recommended citation
Baxter, T. & McAllister, H.A. (2024), 'Alnus hirsuta' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/alnus/alnus-hirsuta/). Accessed 2024-05-25.

Genus

  • Alnus
  • Subgen. Alnus, Sect. Glutinosae

Common Names

  • Siberian Alder
  • Manchurian Alder
  • Hoary Alder

Synonyms

  • Alnus hirsuta f. sibirica (Spach) H.Ohba
  • Alnus incana subsp. hirsuta (Spach) A.Löve & D.Löve
  • Alnus incana var. hirsuta Spach
  • Alnus incana subsp. tchangbokii Chin S.Chang & H.Kim
  • Alnus sibirica (Spach) Turcz. ex Kom.
  • Alnus tinctoria Sarg.
  • Alnus tinctoria var. microphylla Nakai
  • Alnus tinctoria var. mandshurica Callier

Glossary

apex
(pl. apices) Tip. apical At the apex.
glabrous
Lacking hairs smooth. glabrescent Becoming hairless.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
morphology
The visible form of an organism.
orbicular
Circular.
ploidy
Number of chromosomes.
pubescent
Covered in hairs.

Credits

Tim Baxter & Hugh A. McAllister (2024)

Recommended citation
Baxter, T. & McAllister, H.A. (2024), 'Alnus hirsuta' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/alnus/alnus-hirsuta/). Accessed 2024-05-25.

Tree 20–25 m tall. Bark silvery grey to dark brown, smooth. Branchlets dark grey, angular, densely pubescent when young, glabrescent. Buds ovoid, large (especially terminal), stipitate, stipe 2–3 mm, with two dark brown scales, puberulent. Petiole 15–55 mm, densely silky pubescent, occasionally mostly glabrous. Leaves suborbicular to broadly elliptic-obovate, 3–11 × 2.5–9 cm, thick and leathery, abaxially light green or glaucescent, variably hairy, densely to sparsely hispidulous, rarely subglabrous, and often silky hairs on veins, with hairy domatia, adaxially dark green, sparsely villous to glabrescent, base rounded or broadly cuneate, rarely subcordate, margin lobed (to ⅓ width), incised, irregularly toothed, apex obtuse or acute; lateral veins 5–10 on each side of midvein, craspedodromous. Staminate inflorescences 3–5, borne from the apical and upper lateral buds, semi-erect becoming pendulous at anthesis, 15–20 × 5–6 mm over winter, elongating to 100 mm at anthesis. Pistillate inflorescences 2–8 in a semi-erect raceme borne immediately below males, 5–6 × 2 mm, cylindric, peduncle branch 2–3 cm with second order very short, 1–2 mm. Fruit subglobose or oblong, 15–25 × 7–16 mm, bracts 3–7 mm, thick (c. 1.8 mm), base cuneate, apex truncate-obtuse with 5 small even-sized lobes. Nutlet broadly ovate, 3 mm, with papery wings c. ¼ as wide as nutlet. Flowering April-July fruiting July-October. (Li & Skvortsov 1999; T. Baxter pers. obs.).

Distribution  China Heilongjiang, Jilin, Liaoning, Nei Mongol, Shandong JapanNorth KoreaSouth KoreaRussia Sakhalin, Kamchatka, eastern Siberia

Habitat Temperate forests in mountains and hills, 700–1500 m asl, from dry uplands to wet ground along river banks, in grassy bogs and wet flushes.

USDA Hardiness Zone 3-9

RHS Hardiness Rating H7

Conservation status Least concern (LC)

Alnus hirsuta is a common plant in north east Asia that generally grows into a large, upright, pyramidal tree. It is hugely variable across its range but is most readily distinguished by the combination of: smooth silvery-grey to dark-brown bark; leaves usually broader than long and distinctly lobed with a blunt apex, usually green above and grey-green below; and often flowering and fruiting heavily. It is an adaptable species which is known to be genetically variable (Huh & Huh 1999) and found in a range of habitats.

Grey Alder belongs to the Alnus incana complex, a confused group requiring further research. We follow the bulk of contemporary opinion (e.g. Li & Skvortsov 1999; Ren, Xiang & Chen 2010; (Royal Botanic Gardens Kew 2024) in accepting A. hirsuta as the East Asian counterpart of A. incana. A. hirsuta can be reliably distinguished from A. incana by a number of characters. A. hirsuta tends to be a single-stemmed large upright to spreading, often pyramidal tree (occasionally columnar); its leaves are about as long as broad with a blunt apex and more distinct lobing and coarser toothing; it is generally larger in all parts and is more floriferous with longer male catkins and larger fruit. A. incana by contrast is frequently multi-stemmed and suckers freely, is often shorter in stature, and has leaves which are narrower, more evenly toothed and lobulate, as well as shorter catkins and smaller fruit.

Greater complications arise when attempting to classify variation within the species. Over the years many names have been published at one level or another for plants we recognize as Alnus hirsuta – the synonyms above are merely a selection of the more important ones; none are widely accepted today. Many are regional variants which might make sense locally, but when considered together may overlap morphologically and do not add up to a coherent scheme. A. hirsuta is a known polyploid (Rice et al. 2015) but presently there is no clear relationship between ploidy level and other factors. Further research combining morphological, cytological and DNA evidence is badly needed.

A couple of these names for variants have some limited currency, as follows. Firstly A. hirsuta f. sibirica (Spach) H.Ohba and related names (young shoots glabrous or nearly so, leaves narrower, often more deeply lobed and pubescent on veins beneath – but see Chang, Chang & Park (2005) for a critique) has been claimed from Japan and continental NE Asia alongside with the type form. Morphological distinctions are slight, and cytology is confused, with McAllister (pers. obs.) and Fedorov (1969) reporting it as diploid, triploid and tetraploid. Specimens so named can be found in a range of collections including RBG Edinburgh (from BBJMT 87, Honshu 2005), Ness and Arboretum Kalmthout in Europe, and the Holden Arboretum in North America (Royal Botanic Garden Edinburgh 2024; Plantcol 2024). Secondly, Eom et al. (2011) described A. incana subsp. tchangbokii from South Korea (fissured bark, large terminal buds, orbicular leaves with shallow lobes, male catkins 10 mm wide, and fruit 11–14 mm long; no published combination in A. hirsuta). It is clearly different from typical Korean peninsula A. hirsuta, but such characters appear to be similar to those in plants from further north (T. Baxter pers. obs.). Finally, the Japanese A. inokumae is often sunk into A. hirsuta, either as f. inokumae or without trace. A morphologically distinct diploid with real horticultural significance, we provisionally treat it as a full species (q.v.). Plants of the World Online (Royal Botanic Gardens Kew 2024) currently accepts none of these taxa at any level.

In the wild there are numerous putative hybrids including A. × mayrii, reportedly a hybrid between A. japonica and A. hirsuta. These plants need further investigation; on morphology alone they appear to have little to do with Grey Alder apart from hairier branchlets, petioles, and leaf undersurfaces.

In cultivation Alnus hirsuta makes an attractive, hardy and adaptable plant, suitable for a range of conditions. It is a moderately fast-growing species which can grow up to 1 m per year. It is very cold hardy but continental provenances can fare poorly in oceanic climates, and vice versa. It has potential as a street tree with its tolerance of difficult sites, especially those with fluctuating soil moisture and poor drainage. Careful selection of columnar rather than spreading form is advisable for urban areas. It is common in cultivation throughout Europe and North America, having first been introduced to Veitch’s Coombe Wood nursery by Maries about 1879 (Bean 1976). The largest trees in the UK are at Hergest Croft, Herefordshire (23.3 m × 110 cm, 2023) and Howick Hall, Northumberland (20 m × 130 cm, 2019 – Tree Register 2024). It is best propagated from seed although hybrids are not uncommon. A. hirsuta is noted for its excellent timber, suitable for furniture, tools and turning, and also makes fine charcoal (CABI 2018). In spring it is one of the first species to flower, the male catkins being very showy.


'Bled'

A smaller selection (5 m height claimed), recently becoming available in European nurseries (Pépinière AOBA 2024). More information is needed.


'Harbin'

Synonyms / alternative names
Alnus hirsuta PRAIRIE HORIZON™

USDA Hardiness Zone: 3

Alnus hirsuta ‘Harbin’ (PRAIRIE HORIZON™) was introduced c. 2000. Regarded as a handsome tree with strong, upright growth, it originated from the North Dakota State University breeding programme and was the most drought tolerant plant in their trials – it is also fairly tolerant of urban pollution. It will reach 8 m in 18–20 years (NDSU Research Foundation 2022).