Alnus betulifolia
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Credits
Tim Baxter & Hugh A. McAllister (2024)
Recommended citation
Baxter, T. & McAllister, H.A. (2024), 'Alnus betulifolia' from the website Trees and Shrubs Online (treesandshrubsonline.
Genus
- Alnus
- Subgen. Alnobetula, Sect. Bifurcatus
Other taxa in genus
- Alnus acuminata
- Alnus alnobetula
- Alnus cordata
- Alnus cremastogyne
- Alnus djavanshirii
- Alnus dolichocarpa
- Alnus × elliptica
- Alnus × fallacina
- Alnus fauriei
- Alnus ferdinandi-coburgii
- Alnus firma
- Alnus formosana
- Alnus glutinosa
- Alnus hirsuta
- Alnus incana
- Alnus inokumae
- Alnus japonica
- Alnus jorullensis
- Alnus lanata
- Alnus lusitanica
- Alnus maritima
- Alnus matsumurae
- Alnus × mayrii
- Alnus nepalensis
- Alnus nitida
- Alnus oblongifolia
- Alnus orientalis
- Alnus pendula
- Alnus rhombifolia
- Alnus rohlenae
- Alnus rubra
- Alnus serrulata
- Alnus serrulatoides
- Alnus sieboldiana
- Alnus 'Sipkes'
- Alnus × spaethii
- Alnus subcordata
- Alnus trabeculosa
Deciduous shrub to 2–3 m. Bark grey-brown, densely covered with yellow-brown lenticels. Branchlets grey, terete, glabrous. Buds very short stipitate with 3–5 scales, 15 mm long, glabrous. Leaves 8–16 × 4–10 cm, broadly ovate to ovate-elliptic, apex abruptly acute, base obtuse or truncate, usually asymmetric, craspedodromous with 12–14 lateral vein pairs, irregularly and doubly sharply serrate, adaxially subglabrous, abaxially villous only along lateral veins when young, and with hairy domatia, markedly impressed on adaxial surface, petiole 12–20 mm long, only pubescent in furrow. Stipules 2, broadly lanceolate. Male inflorescences single catkins in leaf axils, cylindric in winter maturing to 20–45 × 10–15 mm at anthesis, suberect to pendulous, shortly stipitate, puberulent. Female inflorescences 1–2 in lateral branches above (rarely below) males, 6–10 × 3–4 mm, erect, peduncle 10–30 mm. Fruit 15–25 × 10–15 mm, ovoid, bract apex 5-lobed. Seed 2 in each bract, 3 × 1.5 mm, elliptic, with asymmetrical membranous wings, stigmas persistent. Flowering March. Fruit ripening in October. (Ma et al. 2019).
Distribution China Zhejiang
Habitat On rocky slopes in valleys, 550 m asl
Alnus betulifolia is a recently described species known only from a single population of 15 plants in Dayuantou Village, Chun’an County, Zhejiang Province, China (Ma et al. 2019). It is most similar to A. firma of Japan, but is recorded as being readily distinguished by its small shrubby habit (at least in situ), single male inflorescences held in leaf axils, and females being held apically to the male inflorescences (rarely below) – a feature not found in any other alder. A. firma and A. sieboldiana (also similar) are by contrast small trees or large shrubs with male inflorescences terminal to the stem, often held on short lateral shoots along the stem with the males always terminal to the female catkins. The relationship with A. alnobetula subsp. mandshurica is not known, but the glossy, strongly craspedodromous, ovate leaves with male inflorescences lateral on the stem mark A. betulifolia as significantly different.
As Alnus betulifolia is known only from a single site more research is needed to ascertain if it is more widespread or an introduced plant. Indeed, taxonomic uncertainty hangs over Section Bifurcatus in general, with overlapping morphology between several taxa and many unanswered questions (T. Baxter, pers. obs). As currently understood, however, A. betulifolia is significantly distant from all other Subgenus Alnobetula taxa, separated by over 1000 km from the nearest known A. alnobetula or A. firma. The only species it is conspecific with are A. cremastogyne and A. trabeculosa, two very different taxa. China’s Zhejiang Province does have a number of known relict taxa in the Betulaceae including Ostrya rehderiana and Carpinus tientaiensis, as a result of the ancient sub-tropical forest which occurs in this region and which has previously served as a glacial refugium (Wang 1986). A. betulifolia may fit into this model and would certainly be unable to breed with other alders; it may represent a relict population of a more widespread relative of A. firma from a previous interglacial period.