Conclusion

The analysis of the distribution of chemical characters shows remarkable agreement between primitive pteridophytes (fern allies plus ancient fern families) and gymnosperms. This applies to the widespread occurrence of biflavonoids in the Psilotaceae and Selaginel-laceae, on the one hand, and in the Cycadales and conifers, on the other. In all these groups biflavonoids are based on apigenin and show identical coupling patterns. Also, the rareness of flavonols, flavanones and flavanonols in the primitive families of the pteridophytes and their at least partial absence from the gymnosperms are remarkable. Indeed, both the pterid ophytes and the gymnosperms could be envisaged as sharing the same (psilophytalean?) ancestor, characterized by the presence of fatty ««-hydroxyacids and bi-flavones (two 8.3'- and 6.0.4'-coupled apigenin units), as well as by the relative scarcity of flavonols and tri-terpenoids. The widespread occurrence of oxidative coupling reactions, leading not only to biflavonoids but also to dimerous catechols and dimerous and trim-erous stilbenes, must be an ancient character in the evolution of tracheophytes.

Further chemical evolution of the two major groups was divergent. The pterosinoids and flavonoids of the Equisetaceae are supposed to have evolved parallel to those of true ferns. In advanced families of the pteridophytes triterpenoids are well diversified, as shown chiefly by the presence of many compounds of the ho-pane and cycloartane types. Among their diterpenes kauranes predominate. These always belong to the eni-series and hence do not necessarily show any relationship to the kauianes of the gymnosperms, which mostly belong to the normal conflgurational series. An

Table 3 b. Further selected chemical data for Gymnospermae

Hydroxyacids

Unsaturated adds Polyketides Lignans

Major

Minor

Stilbenes Alkaloids and dimers and other n-cmpds

Table 3 b. Further selected chemical data for Gymnospermae

Major

Minor

Stilbenes Alkaloids and dimers and other n-cmpds

Cyca

16:10,160H

16:9,160H 18:9,10,180H

18:2,3 20:23

Az Am

Stan

Az

Zami

Az

Bo we

Az

Gink

16:10,160H

16:9,160H 16:160H

16:1-3 18:1-4 20:2-4

Py

Arau

16:10,160H

16:9,160H 16:OH

Ll-3 Fl,2 Cl

Taxa

18:2 20:3

LI-3 Di Ta

Ceph

P23

Podo

20:3

Ll-3

Scia

20:3 20:4

Phyl

Taxo

18:1,2 20:3,4

L13 Cl ,2 P2

Cupr

20:3,4

Ll-3 Fl,2 Cl,3 '

Pina

16:9,160H

16:160H 18:9,10,180H

18:1-3 20:3,4

Ll-3, Fl,2 Be PnftiRPcPçPi

Ephe

20:3,4

El-3

Welw

16:10,160H

16:160H 10:100H

R RR

Gnet

16:10,160H

Cy Ac

R RR Pc HR PI

Addenda to Table 3

  1. Glossary of symbols for o-hydroxyacids; number of carbon atoms of the normal fatty acid chain: position of hydroxyls.
  2. Glossary of symbols for unsaturated acids; number of carbon atoms of the normal fatty acid chain: number of double bonds in one or more derivatives; Cy cyclopropane fatty acids (sterculic acid, malvalic acid)
  3. Glossary of symbols for polyketides LI osmundalactone

L2 angiospteroside L3 other simple lactones

4. Glossary of symbols for lignans LI dibenzylbutanediols

L2 dibenzyl-jMactones/ols L3 aryltetralins/naphthalenes

Al acylphloroglucinols A2 methylenebisphloroglucinols Ac acetophenones

Fl arylbenzofurans F2 diarylfurofurans Be arylbenzylfurans

XI mangiferin/isomangiferin X2 other xanthones

CI conioids C2 modified conioids C3 diarylbutadiene

5. Glossary of symbols for 3,5-dihydroxystilbenes Pn pinosylvin Pc

piceatannol (3',4'-OH) hydroxyresveratrol (2',4'-OH)

Underlined symbols refer to partially O-methylated derivatives ft. Glossary of symbols for alkaloids and other N-containing compounds Am a-amino-/?-methylaminopropionic acid E2 ephedradines Az azoxymethanol glycosides E3 oxazolidone/dines

Di )9-dimethylamino-a-hydroxycinnamates Ly lycopodium alkaloids of diterpenoid taxanes PI benzyltetrahydroisoquinolines

E1 ephedrines P2 homoerythrines

P3 cephalotaxines Pa palustrines

«-pipecolines Py pyridines Ta taxiphyllin

Pi analogous situation prevails for pimaranes. Another class of compounds characteristic of advanced pterid-ophytes is constituted by the methylenebisphloroglucinols. With respect to flavonoids, in the advanced pteridophytes flavonols abound and chalcones and flava-nones are common. Representatives of the latter compound types, absent from primitive pteridophytes, ap pear in the gymnosperms only in the Pinaceae, notably an advanced family. Thus it can be said that the primitive chemical traits shared by pteridophytes and gymnosperms may point to their common descent. The similarities acquired during further evolution appear to be due to the action of similar selective pressures exerted upon them.

Rather strong chemical similarities also exist between advanced pteridophytes and angiosperms. With regard to flavonoids these include the presence of flavonols, flavanones, ring-A 6,8-C-methylation and ring-B trihydroxylation. For terpenoids, triterpenes (hopanes, cycloartanes), diterpenes (chiefly kauranes of both stereochemical series, pimaranes, labdanes) and sesquiterpenes can be adduced. Additionally, highly C-methylated phloroglucinols (in Dryopterida-ceae, Rosaceae, Myristicaceae) can be mentioned. Since no relationship between ferns and angiosperms is acceptable, the appearance of these substances in both plant groups is another example of parallelism. The notable chemical agreement between the Gnetatae and some angiosperms, commented upon earlier by us (Gottlieb and Kubitzki 1984), is also pertinent here. The widespread occurrence of parallelism may be explained by postulating the action of common selective pressures, which are related to the plants' defence system.

References

(See also General References to Pteridophytes)

Berti, G., Bottari, F. 1968. Constituents of ferns, In: Reinhold, L., Liwschitz, Y. (Eds) Progress in Phytochemistiy. Vol. 1: 589-685. London: Interscience Publ.

Boralle, N., Braquet, P., Gottlieb, O. R. 1988. Ginkgo biloba: a review of its chemical composition, In: Braquet, P. (Ed) Ginkgolides - chemistry, biology, pharmacology and chemical perspectives. Vol. 1, 9-25. Barcelona: J. R. Prous, Science Publ.

Cooper-Driver, G. A., Haulier, C. 1983. The changing role of chemistry in fern classification. Fern Gaz. 12: 283-294.

Gottlieb, O. R., Kubitzki, K. 1984. Chemosystematics of the Gnetatae and the chemical evolution of seed plants. Planta Medica 50: 380-385.

Hegnauer, R. 1962. Chemotaxonomie der Pflanzen. Vol.1, 220-317. Basel: Birkhäuser.

Hegnauer, R. 1985. Chemotaxonomie der Pflanzen. Vol.7, 398-554. Basel: Birkhäuser.

Soeder, R. W 1985. Fern constituents: including occurrence, chemotaxonomy and physiological activity. Bot. Rev. 51: 442-536.

PTERIDOPHYTES

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