Search

The lipophilic exudates deposited on aerial parts of four species of Cassinia and twelve species of Ozothamnus (Asteraceae, Gnaphalieae) have been analyzed for the presence of flavonoid aglycones and some other phenolics. A total of 55 flavonoids were identified, including several rare flavonols. Flavonols are prevailing over flavones, and 8-O-substitution is dominant in both groups. Ozothamnus rosmarinifolius is exceptional in producing several coumarins. Four dihydrobenzofurans have also been identified from this species. Cluster analysis and principal coordinate analysis of the flavonoid data provide support for combining species of Cassinia and Ozothamnus into a single genus.

The Mediterranean Ononis species, O. fruticosa, O. natrix subsp. ramosissima and O. tridentata, have been analyzed for their exudate flavonoids. More than 20 flavonoid aglycones were identified, some of which are rather rare natural compounds. One of them, namely hypolaetin- 8,3′,4′-trimethyl ether, had been found only once before. The results are presented in a table along with literature data, and the chemotaxonomic impact of the flavonoid patterns is discussed.

Forty-two flavonoids and a stilbene (pinosylvin) were identified in the leaf exudates of 11 temperate species of Nothofagus from South America, Australia and New Zealand. The flavonoid profiles demonstrate significant taxonomic value at the subgeneric level. Most species of subgenus Fuscospora are characterized by the presence of pinosylvin, galangin and galangin methyl ethers. Kaempferol-type flavonols are abundant in subgenus Lophozonia while these flavonols are largely absent from species of subgenus Fuscospora. The flavonoid patterns are largely in agreement with a recent subgeneric classification of Nothofagus.

Leaf and bud exudate flavonoids were analysed for all Eucryphia species, and 28 compounds were identified. Cladistic analyses of phytochemical data indicate that the two Tasmanian species, E. lucida and E. milliganii are sister taxa, which is consistent with morphological studies. Cluster analysis and ordination would suggest that the species E. wilkiei from north eastern Queensland is relatively isolated from other Australian and South American taxa.

Twenty-two species of Scophulariaceae have been found to accumulate flavonoid aglycones externally on their leaves and stems. They belong to the genera Anarrhinum , Antirrhinum , Asarina, Calceolaria, Mimulus, and Odontites. Most of the flavonoids are methylated flavones and flavonols, some with 6-O and/or 8-O -substitution. One of them is the natural isobutyryl ester of a rare flavone.

Representatives of the genera Odixia and Ozothamnus, Australian Asteraceae belonging to the tribe Gnaphalieae, have been analyzed for the presence of flavonoid aglycones accumulated on leaf and stem surfaces. Fiftytwo more or less lipophilic flavonoids have been identified. Methyl ethers of apigenin, luteolin, kaempferol and quercetin are abundant, while rare methyl ethers of isoscutellarein, 8-hydroxy galangin, herbacetin and gossypetin appear to be characteristic. The distribution of rare flavonoids is discussed

A series of Asteraceae, belonging to the tribes Astereae, Eupatorieae, Helenieae and Heli­antheae, have been analyzed for the presence of flavonoid aglycones accumulated on leaf and stem surfaces. Methyl ethers of apigenin, luteolin, kaempferol, and quercetin as well as methyl ethers of their relevant 6 -hydroxy derivatives were abundant, whereas 8 -O-substi-tuted derivatives and flavanones were encountered only occasionally; 6 ,8 -di-O-substituted flavonols were found in only one species.

The flavonoid aglycones excreted by and deposited on aerial parts of 12 species of tribe Eupatorieae, including 10 species of Eupatorium (narrowly defined), Conoclinium coelestinum, and Brickellia eupatorioides, have been analyzed. The flavonoid pattern of Eupatorium is dominated by 6-O-methylated flavones, and there are relatively few differences between species including those of section Verticillata. In contrast, both Conoclinium and Brickellia were found to have significantly different flavonoid patterns. In Conoclinium, this included more highly O-methylated flavones, including the relatively rare compound 5,7,4′-triOH-6,3′,5′-triOMe flavone. In B. eupatorioides this consisted of O-methylated flavonols that are a feature previously reported to be characteristic of Brickellia and thus support the placement of the species in this genus.

Three species of Ambrosia (Asteraceae) were studied for leaf and stem exudate flavonoids. Among these, A. bidentata contained 5,7-dihydroxy-8,4′-dimethoxyflavanone and other rare flavonoids, whereas A. chamissonis and A. trifida were shown to contain a number of trivial flavonoids.

Introduction Most species of Kalanchoe (Crassulaceae) are more or less succulent xerophytes. The large Com­ positae genus Senecio also houses many species with succulent appearance. In both genera the presence of waxy material on their leaf surfaces and also on stem surfaces is rather widespread. In the course of our search for plants producing exu­ date flavonoids (c.f. Wollenweber, 1990) we have studied several species each of both genera. They all were found to be devoid of epicuticular flavo­ noid aglycones, but we happened to isolate some of the triterpenoid constituents forming the “leaf wax” (the term wax being used here in the botani­ cal sense, regardless of the chemical definition; c.f. Barthlott and Wollenweber, 1981). Since to our knowledge externally accumulated triterpenoids have not been reported so far from neither K alan­ choe nor Senecio (Mahato et al., 1991), we studied the major constituents of their leaf waxes. As it turned out the wax does not only appear very sim

A series of methylated flavonols and two methyl flavones have been identified in the exudate of the American gumweed species Grindelia glutinosa and Grindelia robusta. They resemble the flavonoid patterns observed in other species of this genus, which thus shows a tendency for accumulation of methylated flavonols.

Six species of Pelargonium and one species of Geranium were studied for their surface flavonoids. Some of them were found to exhibit an unexpectedly high number of methylated flavonoids, mostly flavonols. The chemotaxonomic significance of exudate flavonoid diversification is shortly addressed.

In the course of continuing studies on the occurrence and chemical composition of lipophilic exudates on plant surfaces, the leaves of Empetrum nigrum have been studied. They were found to produce a considerable amount of lipophilic material which mostly consists of phenolic compounds. We here report the identification of two dioxygenated chalcones, three dioxygenated dihydrochalcones, and two dihydrophenanthrene derivatives. Exept for one chalcone, all these compounds were found for the first time as natural products. The upper and lower epidermis of the rolled hypostomatous leaves bear glandular trichomes. By flavonoid specific staining it can be shown that these natural products are accumulated within the capitate glandular cells.

Six species of Juglandaceae have been checked for the occurrence of flavonoid aglycones on their leaf and fruit surfaces. Except for one, they exhibit flavonols, mostly methyl ethers of kaempferol and quercetin, including 6- O-substituted derivatives. Apigenin and acacetin are the only flavones found so far. Flavonoids accumulated on leaves are different from those excreted on green fruits. It has become evident that in future studies greater attention must be paid to the localization of flavonoid aglycones in different plant organs.

Leaf glands of Ceanothus species excrete a lipophilic material that contains a variety of flavonoids. Most of these are aglycones, but some glycosides were also observed. Seven out of eight species exhibit flavonols, whereas flavones are excreted by only one species. Four species produce flavanones and dihydroflavonols; one excretes a remarkable quantity of flavonol glycosides. The exudate flavonoids thus form different patterns that might be characteristic for different Ceanothus species.

The resinous material accumulated on aerial parts of Madia species is shown to consist mainly of diterpenes, containing a series of flavonoid aglycones. A6- and/or 8-O-substitution is characteristic for many of these flavonoids. Three known rare diterpenes were found and the structure elucidation of a diterpene with a new carbon skeleton, named madiaol, is reported.

Externally accumulated flavonoid aglycones have been found for the first time in Nonea species. They exhibit only flavones, one of thembeing the rare tricetin-4ʹ-methyl ether. Within the subfamily Boraginoideae, exudate flavonoids appear to be a rare character.

The sticky lipophilic exudates produced by glands on inflorescences of Rosa centifolia cv. muscosa and Rubus phoenicolasius contain flavonoid aglycones. Ten different flavonoids were identified from Rosa centifolia cv. muscosa, including several flavones with 6,8 -methoxy substitution. In Rubus phoenicolasius, the major flavonoids are methyl ethers of quercetin.

A new flavonoid, 2,3-trans-5,2′-dihydroxy-7,8-dimethoxy-dihydroflavonol-3-O-acetate, was isolated from the farinose coating on the lower leave surface of the fern, Notholaena sulphurea. The 2,3-cis diastereoisomer was isolated as a co-constituent. This novel acylated flavonoid is characteristic for the chemotype of N. sulphurea exhibiting yellow frond exudate. Its orrurrence underlines the affiliation of the species with the genus Notholaena

The thin waxy coatings on leaves of nine species of Callistemon, two of Melaleuca and one species of Metrosideros, have been studied for the occurrence of leaf surface flavonoids. The Callistemon species and Metrosideros robusta exhibit only C-methylated flavonoids, while O-methyl flavonoids were detected in Melaleuca huegelii. The new natural C-methyl flavonol, 5,7-dihydroxy-3,8,4'-trimethoxy-6-C-methylflavone, was isolated from Metrosideros robusta. The leaf wax of Callistemon coccineus contains the novel C-methylflavonoid, 5,4'-dihydroxy-8-C-methyl-7-methoxy flavanone. (C) 2000 Elsevier Science Ltd.

Seven species of Salvia and one species of Trichostema were analyzed for their exudate flavonoids. They were found to exhibit flavonoid aglycones in various numbers and different patterns. Most of these are flavones, in which 6-methoxy-substituted compounds predominate.

This paper presents a review of the occurrence of tricetin and its methyl ethers, with respect to their occurrence in the free state. In addition to literature data, our tabulated survey also includes a dozen unpublished results. The review indicates that 5,7,3′,4′,5′-pentahydroxyflavone and its methyl derivatives are more widespread than was known so far. Their presence as aglycones has been proved in a good number of plant species belonging to unrelated families.

Exudate flavonoids have been found on the green fruits of Catalpa ovata (Bignoniaceae) and Paulownia tomentosa (Scrophulariaceae) and on the leaf surfaces of Greyia sutherlandii (Melianthaceae) and Paulownia tomentosa, respectively. The flavonoid aglycones are mostly flavone and flavonol methyl ethers, including some rare natural products. Several flavanones and 2 dihydrochalcones have also been detected, the flavanones produced by Paulownia being geranylated products. The occurrence of exudate flavonoids on fruit tissue has been rarely noticed in the past.

Leaves and young twigs of Hypericum balearicum L. exhibit lipophilic glandular products that can be re­ covered by rinsing green aerial parts with acetone. Major components of the resinous material are the triterpenes lupeone and lupeol. The intensely yellow col­ our of the acetone solution is due to a novel natural product, identified as 1,2,5-trihydroxyxanthone.

The leaf exudate of Empetrum nigrum contains, among other phenolic constituents, two novel bibenzyls. These were identified by spectroscopic methods as 3,5,3′-trihydroxy-4-methoxybibenzyl and 3,3′-dihydroxy-4,5-dimethoxybibenzyl.

Ten methylated flavonols have been identified in the lipophilic resinous exudate found on aerial parts of Grin­ delia tarapacana, a gum weed species of Chile.

Aerial parts of Dorema aucheri exhibit a lipophilic exudate material which was shown to contain several flavone methyl esters.

Several species of Nicotiana and Solanum and further members of the Solanaceae have been examined for their exudate flavonoids. Most of the aglycones are widespread flavonols, but rare and unusual flavonols were also found, e.g. in exudates of Physalis and Solanum species. Flavones occur throughout the family, but flavanones are rare. Our data are presented in comparison to previous results. The chemodiversity of the observed structures is discussed in relation to literature reports. Morphological and systematic aspects are briefly addressed.