Flavonoid Variation in Arnica subgenus Arctica

-Twelve flavonoids (including seven flavonol and three flavone glycosides, one flavone aglycone, and one unknown) were isolated from the leaves of 198 populations of the seven species comprising Arnica subgenus Arctica. Flavonoid profiles are relatively simple, with two to six compounds found per population; however, considerable flavonoid variation was apparent in populations of A. angustifolia, A. frigida and A. Ionchophylla. In subgenus Arctica, flavonoid diversity appears to have accompanied high morphological variability. Leaf flavonoid chemistry supports the hypotheses that A. fulgens and A. sororia are very closely related, and A. rydbergii probably represents the most advanced species within the subgenus. Only A. rydbergii is clearly delimitable on the basis of its flavonoid chemistry. The absence of any highly derived or methylated flavonoid suggest the subgenus Arctica probably represents the most ancestral subgenus in Arnica. Introduction Arnica (Asteraceae), a genus of about 28 species, are rhizomatous perennial herbs having simple or branched stems bearing opposite leaves, and large, single or cymose heads of yellow flowers. Maguire [1] has recognized five subgenera within the genus, two of which, Austromontana [2] and Chamissonis [3] have been examined for flavonoid content. Prior to these investigations, little was known about the flavonoids of Arnica [4-9]. Arnica subgenus Arctica has recently been revised to include seven species [10]. These species are widespread between 45 and 80°N in North America, and between 60 and 80°N in the U.S.S.R. Disjunct populationsare also found in northern Scandinavia. The present paper reports results of a study of leaf flavonoids in subgenus Arctica. Previous papers have dealt with the flavonoids ofA. frigida and A. Iouiseana [11 ], A. fulgens and A. sororia [12], and A. angustifolia [13], all of subgenus Arctica. This paper is first to report on the flavonoid constituents of A. rydbergii and A. Ionchophylla ssp. Ionchophylla. Arnica Ionchophylla ssp. arnoglossa was not examined. The base chromosome number for all species is X= 19, with cytotypes of 2n=38, 57, 76 and 95 (Received 24 March 1987) 133 reported [10]. The purpose of this study was threefold: (a) to ascertain whether all taxa in the subgenus are distinguishable on the basis of leaf flavonoids; (b) to report on the flavonoid variation within the subgenus and (c) to determine if the distribution of flavonoids correlates with hypothesized relationships in the subgenus [10]. Results Twelve flavonoids (including seven flavonol and three flavone glycosides, one flavone aglycone, and one unknown) were isolated from 198 populations of the nine taxa surveyed. Flavonoid characterization, and spectral and chromatographic data were carried out according to our previous work [11]. The distribution and frequency of occurrence of the compounds in all populations is presented in Table 1. The flavonoids of the Arnica species examined in this study are all based on apigenin, kaempferol, luteolin and quercetin, Only two sugar moieties, glucose and galactose, are associated with these flavonoids. Sugar linkages are most commonly found at the 3-position in the flavonols and at the 7-position in the flavones. The unknown compound (Table 1) was found in such minute quantities that identification could not be accomplished. The compounds quercetin 3-O-galactoside, kaempferol 3-O-glucoside (astragalin) and quercetin 3-O-diglucoside are T A B LE 1 D IS T R IB U T IO N A N D F R E Q U E N C Y O F O C C U R R E N C E O F IN D IV ID U A L F LA V O N O IO S IN A R N IC A S U B G E N U S A R C T /C A