Wochenendrätsel 74

[JDL]

I enclose a part of my key dd 10SEP2008


Betula L.

(Betulaceae)

Identification key for the species of the genus,
based on vegetative features, from specimens in West-European collections.
Jan De Langhe

(draft and update 10 September 2008)


1 a Shrub AND lamina with ≤6 pair, +/- shallowly lateral veins (rarely some leaves with up to 8 pair of veins). 2

b Tree or shrub. IF shrub, then lamina with ≥8 pair lateral veins, often obvious deeply ribbed. ......................... 7

2 a Margin crenate. Lamina obovate, +/- round or kidney shaped, at least as broad as long, often broader than long. ...... B. nana (Betula/Apterocaryon)

b Margin not crenate, OR variable coarsely serrate to crenate. Lamina sometimes equally broad as long but usually obvious longer than broad. 3

3 a Apex sharp AND margin sharp-pointed toothed. 4

b Apex obtuse to rounded AND margin +/- obtuse-pointed toothed (attend: juvenile or strong shoots can differ in sharper toothed margin and sharper apex). 5

4 a Young shoot brownish glandular (especially on end of shoot, visible with LENS), often sticky to the touch. ..... B. occidentalis (Betula/Betulae)

b Young shoot if glandular then transparent or white (LENS), often densely and short hairy and poorly or not glandular. B. pubescens (Betula/Betulae)

5 a Lamina broad, sometimes almost as broad as long AND margin coarsely toothed or +/- crenate and coarsely toothed. ......... B. pumila (Betula/Apterocaryon)

b Lamina always obvious longer than broad. Margin more regular and finely toothed. 6

6 a Lamina adaxially dark green, ovate to rhombic. Primary teeth +/- broad at their base. ........... B. ovalifolia (Betula/Apterocaryon)

Different: hybrid of B. ermanii and B. ovalifolia, with characters between both parents: +/- deeply ribbed to 8 pairs, base wedge shaped, rounded to cordate, apex sharp to obtuse. B. apoiensis (Betula)

b Lamina adaxially green, ovate to obovate. Primary teeth +/- narrow at their base.
.......................... B. fruticosa (Betula/Apterocaryon)

[JDL]

see here some leaves of Betula nana
quite often more kidney shaped and in first place broader than long
and second place small lamina

[tormi]

Danke Jan,

ein sehr guter Schlüssel und wie immer tolle Bilder.

[JDL]

some images to give a Betula overview

The subgenus Apterocaryon and subgenus Betula with some Betulae

[JDL]

The subgenus Betula with the Asperae

[JDL]

The subgenus Betula with the Acuminatae

[JDL]

The subgenus Betula with the Betulae

[JDL]

The subgenus Betula with the Lentae

[JDL]

and finally

The subgenus Betula with the Costatae, Dahuricae

and the subgenus Nipponobetula

[JDL]

For an overview of the genus Betula as above, it is important
to say that almost all leaves are taken from WILD source material
and from SHORT shoots or from the BASE of LONG SHOOTS

if other leaves are compaired
quite often these are only resembling in part!

[tormi]

Danke Jan,

und wie immer tolle Bilder.

[LCV]

Hi Jan,

I am missing Betula glandulosa in your list. I saw on an American website that B. glandulosa should be the American version of B. nana and some people say, it is a subspecies of B. nana. What is your opinion?

BR Frank

[JDL]

Hi Jan,

I am missing Betula glandulosa in your list. I saw on an American website that B. glandulosa should be the American version of B. nana and some people say, it is a subspecies of B. nana. What is your opinion?

BR Frank

Dear Frank,

It is near to or infraspecific of Betula nana.

Only the most represented taxa are on those sheets.
I also composed a booklet (80 pages), with some more taxa and portrayed like the Betula alnoides and Betula ermanii elsewhere in the forum about Baumlisten here.
I do hope all of this (and my other keys) will be presented on www soon, I am just awaiting green light from the university Ghent (regarding space).
So I could share it with other people (free PDF).

In order to sort out the taxa I should discuss in my key, I of course have contacted the world specialists of the genus Betula

And Hugh McAllister answered me about Betula glandulosa:

"Betula glandulosa - probably arose from a distinct relict population which survived the glacial further south than the normal form of B. nana. Molecular work should sort this out."

Given this, and the fact that this taxon is not that very well represented in cultivation by means of Natural Source material. I decided to not include it (and some other rare or difficult taxa) in my key. After all I would like to keep it as simple as possible: based on vegetative characters and as seen on specimens in European collections.
I do not have the time to investigate the genus much deeper, because other genera are challenging me for the moment.

grts

Jan

[LCV]

Hi Jan,

thank you.

Frank

[Sebastianii]

WOW! Awesome gallery! Thanks a lot, Jan! Gotta save them...