Contribution of Light and Electron Microscopy to Identification of Bark from Frangula azorica, an Azorean Medicinal Plant

Frangula azorica V. Grubow is a Macaronesian flora medicinal plant, endemic from Azores islands and inscribed on the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. This species, known as “sanguinho,” belongs to the family Rhamnaceae, the same as Frangula alnus Mill. and Frangula purshiana (DC.) J. G. Cooper, two widely used official laxative herbal medicines of the western Pharmacopoeias constituted by the dried barks of each species. Morphological and chemical studies on F. azorica dried bark are scarce although it is potentially recognized as a Portuguese laxative herbal medicine. Macroscopically, the bark occurs in quills or nearly flat pieces. A channeled external surface with transversely elongated lenticels is characteristic. When the outer phellem layer is removed, a bright purple inner phellem layer is disclosed. Light and electron microscopy observations revealed flattened phellem cells with slightly thickened walls, cortical parenchyma with secretory ducts and groups of sclereids, phloem with groups of fibers and sheaths of parenchymatous cells containing druses or more frequently prismatic crystals of calcium oxalate, and parenchymatous medullary rays one to three cells wide with spherical starch grains. Observation of these botanical characteristics must be included in quality monographs of F. azorica bark herbal medicine.

The perennial Macaronesian species of Bubonium (Compositae - Inuleae).

Six perennial Macaronesian species are recognized in Bubonium J. Hill emend. Briq.: the Cape Verdian B. daltonii (Webb) T. Halvorsen, with two subspecies, ssp. daltonii and ssp. vogelii (Webb) T. Halvorsen, and B. smithii (Webb) T. Halvorsen; and the Canarian B. intermedium (DC.) T. Halvorsen & Wikl., B. graveolens (Forssk.) Maire, with two subspecies, ssp. odorum (Schousb.) Wikl. and ssp. stenophyllum (Link) T. Halvorsen, B. schultzii (Balle) Sventenius and B. sericeum (L.f.) T. Halvorsen & Wikl. Four Mediterranean annuals are superficially treated for Macaronesia: B. aquaticum (L.) Hill, Asteriscus maritimus (L.) Less., A. hierochunticus (Michon) Wikl., and A. spinosus (L.) Sch. Bip. A key to the Macaronesian Bubonium species is provided. The chromosome number n=7 is reported for all the Bubonium species in Macaronesia; in B. graveolens ssp. odorum, B. daltonii ssp. vogelii, and B. smithii for the first time. The chromosome number n=6 is confirmed for Asteriscus maritimus. The self fertile annuals are not cross compatible with the other species. Among the predominantly self incompatible perennials internal barriers to gene exchange are weak. Only B. schultzii seems genetically isolated. Between the other perennials the crossability is complete and hybrid fertility high between species from the same archipelago, but reduced between species from different archipelagos. The present occurrence of the Canarian species B. sericeum and B. intermedium and the Cape Verdean B. daltonii and B. smithii seems relict. These frutescent endemics probably belong to an old element in the Macaronesian flora.