Fig. 1. Sorbus aucuparia L., morph 1 (Finland, Helsinki, Länsi-Pasila, 2003).
– Image: Harri
Harmaja (two leaves from the same tree, scanned when fresh).
–
In Helsinki, some trees in fairly natural habitats deviate from the common
pattern in producing leaves possessing leaflets with almost or totally entire
margins. This kind of leaves are produced especially near the inflorescences in
normal dwarf twigs. Within a single leaf, the lowermost leaflets tend to be the
less toothed and entire ones. The teeth of the leaflet margin, when present, are
small, single, and present towards the apex of the leaflet. This plant is not readily referable to any of
the three intraspecific taxa of the rowan, or European mountain ash (S. aucuparia, Rosaceae) mentioned in the current Finnish floras.
Rowan trees that possess leaflets with partly entire
margins occur in South Finland. I have seen such trees in a high proportion of
all rowans in rocky areas of Helsinki, not far from the sea coast. The entire
part of a leaflet is situated basally and extends from ca. 20 % to approximately
50 % of the length of the leaflet. The name S. aucuparia ssp. aucuparia
var. heteromorpha (Brenner) T.Raatik. most probably applies to this kind of
trees. The plant of Fig. 1 most probably represents an extreme of
the variability of that variety. However, the main distribution of
var. heteromorpha is given somewhat continental and eastern, not coastal, in the country.
According to my field observations, leaflets with more
or less entire margins tend to be somewhat thick, to have small and
strictly single teeth, scantier hairs especially above (sometimes even being glabrous
on their upper surfaces), and a
somewhat glaucous underside. The leaflets of the so-called
typical rowan (S. aucuparia ssp. aucuparia
var. aucuparia) are serrate practically to their very base, tend
to have a thin lamina, fairly large teeth (which may be slightly doubly), distinct indumentum, and often a pure green underside (for
comparison purposes, leaves that are produced by short twigs near the
inflorescences, in not too young trees, should be used). These leaf characters
are indeed roughly the same which are given in the literature for var. heteromorpha
and var. aucuparia, respectively.
Interestingly, all rowan trees cultivated for
ornamental purposes in parks and street sides in Helsinki that were checked by
me, appear to represent var. heteromorpha.
Fig. 2. Sorbus aucuparia, morph 2 (Finland, Nurmijärvi, Perttula, 2003). – Image: Harri Harmaja (fresh short twigs, scanned directly). – The leafs and leaflets are less than half of the size of those of typical rowan. The leaflets are 11-19 ´ 4-7 mm in size, indistinctly doubly serrate, greyish-green, beset with rather long hairs on both sides. The few small individuals that formed the stand seemed normally developed.
Fig. 3. Sorbus aucuparia, morph 3 (Finland, Helsinki, Länsi-Pasila, 2003). – Image: Harri Harmaja (scanned from fresh leaves). – The terminal leaflet is deviating, being large and having coarse teeth or shallow lobes. Only a minority of leaves were of this kind, in most of them mainly differ from typical rowan through the terminal leaflet which is fairly large and broader than the other leaflets. The leaves are almost glabrous, dark green, paler on underside. The leaflets had distinct, mostly single teeth. This kind of leaves are not referable to any of the known intraspecific taxa of the rowan known in Finland. The variability displayed in this figure is hardly interesting taxonomically as this kind of leaves are commonly born in rapidly developed long shoots in which the stipules are often well-developed.
Fig. 4. Sorbus aucuparia, morph 4 (Finland, Siuntio, Hollstens, 2004). – Image: Harri Harmaja (scanned from fresh leaves). – The leaves of this plant are scantily hairy, display chlorophyll deficiency at marginal areas of the leaflets, have mostly rather narrow leaflets, and also appear deviating in a few other respects. A group of small trees of this kind were found in somewhat rich, apparently sowed and fertilized spruce woods. The appearance of these leaves may result from developmental disorders caused by the chemicals used in the supposed fertilization.
Created March 17, 2004. Latest revision July 9, 2004.