A New System of the Genus Betula L.—the Birch
A. K. Skvortsov
Bull. Mosc. Natur. Soc. 2002, Otd. Biol., v. 107 (5): 73–76
The literature treating the systematics of the birches is quite extensive.
However, most of it is dedicated to problems of species size, species delineation, or descriptions of new species and
interspecific hybridization studies.
The author of this article has been tackling the same range of problems for many years mostly on the
material collected in northern Asia.
These, however, represent only a part of the genus, that is, undoubtedly, its youngest part.
While studying material for the new Flora of China (1999), the authors noticed deficiency
and inadequacy in the infrageneric systematics of the genus Betula. Being time restricted by the project deadlines,
the co-authors (Li Peiqiong and the author of this article) decided to refrain from delineating any infrageneric groups.
J. J. Furlow, the author
of Betulaceae treatment in the Flora of North America (1997), did not provide any infrageneric grouping,
either—and probably for the same reason. Here I am trying to fill out this gap while relying on my previous work.
In 1865 E. Regel proposed the division of the genus in 7 sections 
1. Albae (B. alba L. sensu latissimo with 9 subspecies and B. microphylla)
2. Fruticosae (B. fruticosa, B. middendorffii)
3. Nanae (B. nana, B. michauxii, B. glandulosa, B. pumila, B. humilis)
4. Dahuricae (B. dahurica)
5. Costatae (B. schmidtii, B. nigra, B. ermanii,
B. grossa, B. utilis, B. corylifolia)
6. Lentae (B. lenta, B. alleghaniensis)
(B. cylindrostachya, B. alnoides,
Here the Fruticosae/Nanae parts look particularly inadequate. Also, the section Costatae appears quite
superficial, since the author dumped there all exotic species that were poorly known in Europe at the time.
Regel outlined the sect. Lentae basing on the fact that B. lenta retains its pistillate aments
intact into the winter season, which he considered somewhat reminiscent of Alnus.
The next important step was made by C. K. Schneider (1915, 1916).
While working on Plantae Wilsonianae, Schneider had at his disposal vast newly
collected material, particularly from East Asia. He divided the section Costatae in 7 subsections:
1. Nigrae (B. nigra alone)
2. Corylifoliae (B. corylifolia alone)
3. Asperae (B. schmidtii and B. medwediewi—with a question mark)
4. Ermannianae (B. ermanii, B. utilis, B. albo-sinensis, B. jacquemontii)
5. Grossae (B. grossa, B. fargesii, B. insignis, B. globispica, and—with a question mark—B. costata)
6. Lentae (B. lenta, B. alleghaniensis)
7. Chinenses (B. potaninii, B. delavayi, B. chinensis)
However, while proposing his new system for the genus, Schneider at the same time confessed: "Eine wirklich zeitgemäße
Bearbeitung der Gattung Betula fehlt": "There is no
adequate contemporary treatment of the genus Betula" (1915: 312), which enables us to conclude that he was not really
satisfied with his own system. Indeed, his subsection Grossae consisted of three or four components that were not closely related,
while the obvious close relation between B. grossa and the American B. lenta was not depicted at all.
Subsect. Chinenses also appeared heterogeneous; a close relationship between B. dahurica and B. nigra was not
noticed; the peculiarity of B. corylifolia was underestimated as it was considered only in the rank of the subsection,
and so on.
T. Nakai (1915) and V. N. Vasilyev (1969) proposed a few subgenera, but those were essentially rank-changing proposals,
once again based only on material from northern Asia. These proposals did not constitute much progress.
Finally, a recent treatment by Z. D. Chen (1994) has been a kind of step back from Schneider's system.
Chen proposed five sections (no subgenera, neither subsections). Of these five, three remained the same as those proposed
Schneider and other authors (Betulaster=Acuminatae, Betula, and Humiles); however, the majority of
birch species are confined in two extremely heterogeneous sections: Costatae (B. medwediewi, B. raddeana, B. albo-sinensis,
B. austro-sinensis, B. ermanii, B. costata, B. corylifolia, B. nigra, B. alleghaniensis, B. lenta) and Chinenses (B. insignis, B. delavayi,
B. potaninii, B. calcicola, B. globispica, B. schmidtii, B. chinensis).
Therefore, Schneider's statement of 1915 about the absence of a truly contemporary system
for the genus Betula remained valid as late as the end of the 20th century.
Here I dare to bring to my colleagues' attention a system of mine. It is an honor for me to publish it in the same journal
where E. L. Regel
once published his fundamental works on the systematics of the birches.
I have been studying herbarium material in the following depositories:
Moscow (MW, MHA), St. Petersburg (LE), Tomsk (TK), Vladivostok (VLA), Baku (BAK), Batumi (BAT),
Yerevan (ERE), Tbilisi (TBI), Cambridge (A, GH), St. Louis (MO), New York (NY), Beijing (PE), Kunming (KUN), Dehra Dun (DD),
Vienna (W), Kórnik (KOR). In 1960's we received a representative selection of Japanese samples from the
Makino Herbarium (MAK) by exchange. I had opportunities to observe nearly all of the birch species native on the former
USSR territory (except B. maximowicziana) as well as species of the Indian Himalaya and North America in their natural habitats.
Observations of cultivated trees proved to be rather useful, particularly, those made at the Main Botanic Garden (GBS) in
Moscow, the Central Botanic
Garden in Kiev, the Arnold Arboretum in Boston, and the Dendrogarden in Pereslavl-Zalessky.
Genus Betula L.
Type species: Betula alba L. (syn. B. pubescens Ehrh.)
The type specimen of the species B. alba was cited in the literature many times. Recently it has been officially
designated. This is # 1109–1 of the Linnaeus Herbarium (LINN) (Holub 1989: 40; more about B. alba typification in: Vasilyev 1964).
I propose to distinguish four subgenera in the genus, two of which, monotypic, are being first described here.
1. Betula subg. Sinobetula A. Skvortsov subg. nov.
Plants appear to be without resinous glands. Leaf petioles very short (5–12 mm); leaf blades large (to 120 × 80 mm); lateral
to 18 pairs, straight, conspicuously impressed; leaves below densely covered with fulvous-brown tomentum. Staminate aments
unknown until now. Pistillate aments cylindric, in clusters, developing from terminal buds; bracts three-parted nearly to
bract lobes oblong to linear. Fruits small, round, their wings obsolete.
Typus (designated here): B. gynoterminalis Hsu et C. J. Wang 1983 in Acta Bot.Yunnan. 5(4): 331,
So far there is the only one species known, which has been collected only once: Yunnan,
Gongshan Xian, altitude 2,600 m, Sept. 26, 1956. P. Y. Mao N 00521. KUN(!)
This amazing, truly unique birch would fully deserve a rank of a separate genus in case there were anything unusual
about its aments. But they appear to be just normal birch aments, though their location is very peculiar for a birch (which
in the species name).
Therefore, I find it optimal to assign a rank of the subgenus. The description is based on the single specimen so far available,
which is preserved at the Botanic Institute in Kunming, where I've had an opportunity to examine it.
2. Betula subg. Nipponobetula A. Skv. subg. nov.
Syn. sect. Costatae subsect. Coryfoliae C. K. Schneider 1916 in Pl. Wilson. 2: 463.
Trees. Leaves below glaucous, without resinous glands; lateral veins straight, directed towards denticle apices.
Scales of staminate aments imbricate, their apices acute, more or less deflected, pilose.
Pistillate catkins cylindric to ovoid, without glands; bracts three-lobed, but with a single fruit per bract.
Fruit compressed, nutlet round to broadly elliptic, its apex grades into style.
Style up to 3 mm long, with two stigmas.
Typus (designated here, the only species so far known): B. corylifolia
Regel et Maximowicz 1865 in Bull. Soc. Natur. Mosc. 38(2): 417 et tab. 8 fig. 1–3.
This birch is endemic for Honshu, though it is not so rare there (I've seen about 30 herbarium specimens total.)
Though it had always been treated as a distinct species, that was Schneider who made a step ahead and promoted it to
the rank of the subsection. Peculiar leaf shape and venation
different from the rest of the birches and—still more
important—the fruit structure featuring rounded flattened nutlet with a pronounced style embraced by
wings—these are the characters confirming the treatment of the species as a separate evolutionary line that
has never developed any further.
3. Betula subg. Asperae Nakai 1915 in Fl. sylv. Koreana 2: 25
corrected (expanded) A. Skvortsov.
Typus (designated here): B. schmidtii Regel
While Nakai assigned just a single species B. schmidtii to this subgenus,
I place the following three sections here: Asperae (Nakai) Kuzeneva
(which corresponds to Nakai's subgenus); Chinenses (Nakai) Chen, and Lentae
Regel emend. A. Skvortsov. The name Chinenses Nakai would be also
appropriate for this subgenus, but I am choosing Asperae not only due to priority considerations,
but also because the subgenus contains species other than Chinese.
The subgenus differs from the subg. Betula (in the meaning proposed here)
in two most important characters: lack of true-birch, layered bark as well as the structure of the fruit.
We are going to discuss the latter in detail now.
Traditionally birch fruits have been depicted as nutlets with wings.
It is only by the wing-to-nut width ratio that they differ from one another.
Meanwhile, it is the very nature of wings that varies.
The difference is particularly obvious when one compares a fruit of a birch belonging to the sect.
and a fruit of one from sect. Betula
The former has its entire ovary compressed; its wings constitute the part of the ovary that is not filled by the nutlet.
The wings in the latter are special outgrowths on both sides of the ovary.
In the former case, the wings proceed onto the styles; in the latter, they do not reach the styles.
This is a very minute, but constant and meaningful difference. In addition to that, the wings
are nearly concolorous to the nut and not transparent; usually they are rather concave,
so that one can sometimes distinguish their adaxial and abaxial side. In the subg. Betula
usually flat, so that one cannot identify adaxial and abaxial sides.
Unfortunately, the authors of morpho-anatomic treatments of the birch fruit, I. A. Korchagina (1974)
and G. Natho (1976) did not pay attention to the details described here above.
Subg. Asperae has other diagnostic characters, though they may be more or less pronounced and
sometimes appear within the subg. Betula:
— leaves on the elongated branches are smaller and narrower than those on the spurs (including the fruiting spurs);
— pistillate aments are nearly sessile or on short and stout (ca. 2 mm thick) stalks that are frequently densely pubescent;
— there are up to 3 fully developed leaves at proximal parts of fruiting branches; however, there are no buds in the axils
of these leaves; branches that produce pistillate aments then die off;
— pistillate aments do not fall apart while disseminating seed, but rather after that, sometimes persisting until the next
— lateral lobes of bracts in the subg. Asperae are mostly the same width as the central part, nearly not reclining.
The composition of the subg. Asperae Nakai:
Sect. Asperae (Nakai) Kuzeneva 1936 in Flora URSS 5: 280
Typus: B. schmidtii Regel
B. fargesii Franch.
B. potaninii Batalin
B. calcicola (W. W. Smith) P. C. Li
B. chichibuensis Hara
Sect. Chinenses (Nakai) Z. D. Chen 1994 in Acta Phytotax. Sin. 32(2): 137
Typus: B. chinensis Maxim. (syn. B. liaotungensis Baranov)
B. delavayi Franch.
B. globispica Shirai
Sect. Lentae Regel 1865 in Bull. Soc. Natur. Moscou 38(2): 397
Typus: B. lenta L.
B. alleghaniensis Britt.
B. grossa Sieb. et Zucc.
B. insignis Franch.
(syn.: B. kwangsiensis Metcalf, B. kweichowensis Hu, B. austro-sinensis Chun)
B. medwediewi Regel (syn.: B. megrelica D. Sosnovsky)
4. Betula subg. Betula
Typus: B. alba L.
Critical characters of the subgenus: presence of "the birch bark", which is most pronounced in the species
belonging to sect. Costatae and Betula; pistillate aments on slender (about 1 mm),
usually glabrous leafy stalks; axils of stalk leaves usually bear buds, which prolongs the life span of the fruiting branch.
Upon seed ripening, the aments tend to completely disintegrate (though occasionally bracts may persist after seed ripening);
fruits bear wings: outgrowths of the lateral ovary parts; these outgrouths don't reach to the proximal parts of styles;
bract lateral lobes usually differ from the central part of the bract, often reclining sidewards.
The composition of the subg. Betula:
Sect. Acuminatae Regel 1865 in Bull. Soc. Natur. Moscou 38(2): 397
Syn. sect. Betulaster (Spach) Regel 1868 in D.C. Prodr. Syst. Natur. 16(2): 179
Typus: B. alnoides D. Don
B. cylindrostachya Lindl. ex Wall.
B. luminifera H. Winkl.
B. maximowicziana Regel
B. alnoides is different from the rest of the birches by its autumn flowering time and distribution
within tropical/subtropical area. However, its niche there is quite similar to that of our northern birches.
In the eastern Indian Himalaya, near Kalimpong, I have watched its seedlings en masse conquering a fresh landslide,
while mature trees were growing nearby forming a nearly pure, one-species white-trunk grove.
This section is hardly represented on the territory of Russia (by B. maximowicziana).
Sect. Dahuricae Regel 1865 in Bull. Soc. Natur. Moscou 38(2): 396
Typus: B. davurica Pallas
B. nigra L.
I strongly believe that the American river birch B. nigra is closely related to B. davurica.
Both have strikingly similar trunks with exfoliating bark and bright yellow layers underneath these rags.
Early fruit ripening that is typical of B. nigra is to some extent characteristic of B. davurica, as well;
however, B. davurica appears not to be restricted to banks of water bodies the way it is the case
with B. nigra.
Sect. Costatae Regel 1865 in Bull. Soc. Natur. Moscou 38(2): 396
Typus: B. costata Trautv. (syn. B. nikoënsis Koidz.)
B. ermanii Cham. s. l.
B. albo-sinensis Burk.
B. utilis D. Don
B. jacquemontii Spach
This section is fully confined to temperate East Asia, its representatives
dominating forest plant communities at times.
Sect. Apterocaryon Spach 1841 in Ann. Sci. Natur. 15: 195
Syn. sect. Humiles W. D. Koch 1844 in Synopsis Fl. German., ed. 2: 761
Typus: B. michauxii
B. fruticosa Pall.
B. ovalifolia Rupr.
B. glandulosa Mich.
B. nana L. s. l.
B. pumila L.
Here also belong all kinds of local infraspecific taxa as well as hybrids, which makes the section boundary vague.
At any rate, this is a young section, which probably originates either from Costatae or Betula.
Many authors have tried to divide it in two, grouping races
around B. nana and B. fruticosa.
Of course, round small leaves of B. nana are captivating.
However, on a single B. pumila plant, one may find a transition from elliptic leaves
that have denticles of the fruticosa-type, to small rounded ones with roundish
denticles. B. pumila is, kind of, connecting both cycles in one entity.
Syn. sect. Pterocaryon
Spach 1841 in Ann. Sci. Natur. 15: 185 
Typus: B. alba L.
These are our white-bark boreal birches. Even though reversemutants—specimens
with dark bark—are not infrequent among them, the bark always remains layered.
The group is a young one, phytosociologically very active, and rather polymorphous as regards characters.
The amount of species attributed to this group is astounding. However, at a glance, one can distinguish three
essential groups (which may be considered as series):
B. pendula Roth
B. populifolia Marsh.
B. alba L.
B. papyrifera Marsh.
B. occidentalis Hook.
B. raddeana Trautv.
B. tianschanica Rupr.
B. microphylla Bunge
Relationships of the subgenera and sections might be approximately depicted as in Fig. 2.
The subgenus Betula is by all means the youngest. If we try to derive it from another subgenus,
then that other one should be Asperae. Or else it might have had some different ancestors that haven't survived.
The author is deeply grateful to all the colleagues from the institutions named in the text.
A special thank-you to my long-time assistant M. V. Kostina for typing of the manuscript.
This article was completed with financial support of RFFI (Grant # 99–04–48202).
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Translation I. Kadis
19 Dec 2004