Native Cotoneasters of Estonia. (summary)
Traditionally only two species of Cotoneaster have been identified in Estonia. However, the paper of Bertil Hylmö (1994) incited to investigate the Cotoneasters of Estonia on a new level and by now at least 10 taxa of Cotoneaster known to exist here. They are probably apomictic. On the basis of hybridising experiment of Estonian taxa made at Tallinn Botanical Garden a conclusion can be made that they must be pseudogamic. Fruits of Cotoneaster develop only from pollinated flowers, also, if the pollinated flower and pollen belonged to different taxa (either with black and red fruits). In natural communities in Estonia where different taxa of Cotoneaster are growing, no intermediate forms have been detected. The differences between taxa have found proof in the cultivation process at Tallinn Botanical Garden. There are some new taxa, which have not yet been scientifically described – the names of these species are between quotation marks, all the undescribed taxa do not have an author.
In Estonia Cotoneasters grow mostly in alvar forests and in open alvars, some finds are also from subcoastal sandy-stony (acid) areas. Cotoneasters are native only in N and W Estonia. Distribution of taxa is given in Figures 1 and 2.
In Estonia only two series of section Cotoneaster of genus Cotoneaster have been found. Under the series Cotoneaster (red fruits), C. scandinavicus is the most common. It has two obviously ecological forms: f. alvarensis – more robust, with shoots warped downward and f. repens – it grows on open alvars but also in (thick) alvar forestsand seems to be close to C. cinnabarinus. C. scandinavicus ssp. osiliensis is an erect shrub. Differences between C. aff. integerrimus s.str and the typical form are not clear. C. “vaccinoides” is an undescribed taxon with willous leaves on the upper surface and long procumbent branches.
In series Melanocarpi, the occurrence of C. niger has been proved in two localities (probably occurs more often). The most common of this series is obviously C. rannensis (description of species: Hylmö, Fryer 1999). It is common on cliffs vicinity of Tallinn (habitat of holotype). In Saaremaa and south of Tallinn a probably close taxon C. rannensis var. osiliensis can be found. Its inflorescence is smaller. C. aff. ignavius is obviously a morphologically parallel form of this endemic species of Central Asia.
Between these series are two taxa. C. canescens is mostly an erect shrub and C. “semperflorens” an ascending shrub. Fruits of C. “semperflorens” are darker than the fruits of C. canescens.
C. lucidus has naturalised in and near settlements all over Estonia.
We can call special attention to apomixis or the probable and very rare hybridisation of Cotoneaster. In stressing apomixis we can find many undeterminable species all over the area of the genus. Some Cotoneasters in East Siberia are morphologically very close to C. rannensis. When emphasising hybridisation (Fig. 3) we must evidently join most of the classic taxa in Europe to one species and C. integerrimus s.lat., C. niger s.lat. and C. tomentosus can then be only subspecies of the same species.