Abstract

Lubienski, M. 2003. Equisetum ×mildeanum Rothm. (E. pratense Ehrh. × E. sylvaticum L.), en snellehybrid ny for Norge. Blyttia 61: 171-178.
Equisetum ×mildeanum Rothm. (E. pratense Ehrh. × E. sylvaticum L.), a hybrid horsetail new for Norway.

Equisetum ×mildeanum Rothm., the hybrid between Equisetum pratense Ehrh. and Equisetum sylvaticum L. was described by Rothmaler (1951) based upon material that he collected on the baltic isle of Rügen in northeastern Germany. Since that time E. ×mildeanum was only recently found in the Scottish Highlands (Page 1988 & 1997, Wardlaw, Sykes & McHaffie 2001). Plants of this parentage have never been authenticated from Norden (Fennoscandia and Iceland; Borg 1967, Øllgaard & Tind 1993, Øllgaard 2000) or other regions in the holarctic belt (Hultén 1950, Hultén & Fries 1986, Jalas & Souminen 1972, Hauke 1993). Records from several German provinces extending to Poland («Hassia, Holsatia, Saxonia, Prussia, Silesia…», Rothmaler 1951, Meusel et al. 1971) have not been verified or recently confirmed. Rothmaler’s (1951) record for Russia, to which Duckett & Page (1975), Derrick et al. (1987) and Page (1990) possibly refer should be rated equally. This could also be true for the doubtful rated records for Czechoslovakia and Poland by Derrick et al. (1987) also probably drawn from Rothmaler (1951). The repeatedly mentioned occurrence of E. ×mildeanum in Sweden (Duckett & Page 1975, Page 1990 and Øllgaard & Tind 1993) is not specified and perhaps based upon Almquist & Björkman (1960), who listed E. pratense × sylvaticum for the Swedish province Dalarna. According to Borg (1967) it represents a modified E. sylvaticum caused by a disturbed habitat. Borg (1967) nevertheless found a suspicious plant in Finland, which, according to his description, is likely to be the hybrid.

E. ×mildeanum was found in July 2001 in a side valley of Gudbrandsdalen (east of Fåvang, Prov. Oppland) in Norway, which seems to be the first reliable record for this country (fig. 1). The site is a westfacing slope (inclination of approx. 40°) at 600 m along a wood-path at the northern flank of Tromsa valley, southeast of Brekkom (UTM grid reference NP 717.136). The plants were associated with E. pratense, E. sylvaticum and E. arvense. On the slope below the path, consisting of marshy woodland, E. variegatum and E. scirpoides were present. Plants of intermediate morphology occurred scattered within a range of approximately 7 × 2.5 metres. To confirm the diagnosis the Norwegian plants have been compared with material from the Scottish Highlands (Caenlochan, Perthshire) and the type collections of Rothmaler. Plants in both cases fit with the ones collected in Gudbrandsdalen. The type locality on the isle of Rügen between the town of Sassnitz and the cretaceous cliffs at the northeastern end of the Jasmund peninsula (Mecklenburg-Vorpommern, Germany), known as «Stubbenkammer», was earlier visited in June 2000. Although both parent species were found scattered throughout, even growing together, no hybrid was observed.

Because of the morphological plasticity that characterizes horsetail taxa in general, it is indispensable to check the quality of the spores in order to separate mere growth forms from true hybrids. Unfortunately fertile shoots have never been observed in Equisetum ×mildeanum in the wild (Rothmaler 1951, Stace 1991, Page 1997) and were also absent in Gudbrandsdalen. Table 1 compares the diagnostic characters of E. ×mildeanum and its parents. A useful feature to distinguish the three taxa from each other is the branch teeth. Being short-deltoid and not spreading in E. pratense and long-acuminate and spreading in E. sylvaticum, they show intermediacy in E. ×mildeanum: short-deltoid (branches of 1st degree) and long-acuminate (branches of 2nd degree, when present). All branch teeth of the hybrid do not tend to spread. It is wise to pay attention to the problem of atypically modified growth forms of the parents resulting from non-sufficient ecological conditions when searching for E. ×mildeanum. Sometimes, even growing intermixed, these modifications do not differ in any other character from typical representatives of the two species and are in all cases clearly separable from each other. They have already been named by ancient botanists: E. sylvaticum var. pauciramosum Milde and E. pratense var. pyramidale Milde or var. ramulosum Milde (Milde 1867).

Marcus Lubienski, Wodantal 28, 45529 Hattingen, Germany, marcus.lubienski@gmx.de

Blyttia 61 (3)
Blyttias hjemmeside
Lagt ut 24.10.2003 JW