Aemula

Abstract: The phloroglucinols of Dryopteris aemula from the Azores and from Brittany (France), D. azorica and D. crispifolia, a new tetraploid species endemic to the Azores [8], have been investigated. The following two species recently analysed with insufficient amounts of material have been reinvestigated using improved methods: D. maderensis and ‘D. dilatata’ from Tenerife, a new species endemic to the Canary islands and described by Gibby et al. [8] as D. guanchica Gibby & Jermy. We have now found that both these species also contain much albaspidin, particularly the homologue BA. Former results for these and other species differing in some details were corrected (see Table 1) after careful re-examination of the old chromatograms. D. aemula from all origins contains relatively large amounts of two new compounds: aemulin (1) and trisaemulin (20), the structures of which were proved by degradation, NMR.- and mass-spectroscopy. Trisaemulin was present as a mixture of two homologues BBB and BAB. The latter is the first three-ring phloroglucinol found in nature which carries an acetyl group in the middle ring. So far only butyryl-groups were found in this position. D. azorica is diploid like D. maderensis and D. intermedia and all 3 taxa contain practically the same range of phloroglucinols. These facts are in agreement with conclusions based on morphology and cytology, which suggest that these three taxa are essentially conspecific. D. crispifolia contains the same phloroglucinols as D. dilatata s. str.; ths is a further example showing at occasionally different species produce te same compounds. ‘D. dilatata’ from Tenerife differs from D. dilatata s. str. chemically not only by the absence of para-aspidin, but also by the presence of the albaspidins-2 and -3. In the same way it differs of course from D. crispifolia. This is a welcome confirmation of the morphological results [8], showing that D. crispifolia is really different from ‘D. dilatata’ from Tenerife, although it is difficult to differentiate pressed fronds of these two species. Chemical results (see Table 1) are best compatible with the assumption that D. dilatata s. str. may have had its origin from a hybrid of D. assimilis x D. maderensis (= D. azorica = D. intermedia) with subsequent doubling of its chromosomes. They also would be compatible with the possibility that D. crispifolia has arisen from D. aemula and D. azorica in a similar way, provided the latter had suppressed formation of margaspidin and aemulin present in D. aemula but absent in D. azorica and D. crispifolia. No simple rationalisation is yet possible to explain the chemical results for ‘D. dilatata’ from Tenerife with the phloroglucinols present in its putative ancestors.