Rolf M.T. Dahlgren 1932-1987 Professor of botany inUniversity of Copenhagen. Published his original versionof his system in 1975. Most notable classificationsystem in the resent history.
Major interest= evolutionary characters within theangiosperms(class Magnoliopsida) Used a two dimensional graphicsystem(Dahlgrenogram/bubble diagrams) to displayhis phylogenetic system. Dahlgren himself was much interested in phylogeny. Mostly morphological and phytochemical charactersconsidered. Used the “-iflorae” endings in his superorders.
Characters concidered.. Apocarpy,syncarpy & monocarpy conditions Choripetaly,sympetaly & mono-aperaturate pollentypes Sclered idioblasts Types of microsporogenesis Bi and uni-tegmic ovules Presence of raphids,silica bodies Presence of various alkaloids & flavonoids etc.
Dahlgrenogram Diagrams representing a cross section of aphylogenetic tree. Groups are represented by bubbles of different sizesbetween which relationships are implied-though notclearly shown. Much used to display results of broad surveys ofvariation of characters.eg- the types of plastids in thesieve tubes More closely related to Bessey’s cactus-like diagram
Angiosperms (class Magnoliopsida/class Angiospermae)subclass-Magnolideae subclass-Lillidae-represent dicotyledons -represent monocotyledons24 super orders 07 super orders80 orders 26 orders346 families 92 families
Merits and demerits.Merits• Angiosperms are given a more agreeable rank.• No family of angiosperms is left unplaced.• Dahlgrenograms ,-useful to show relationship of superorders,orders &families.-show relative numbers of each group.-useful to compare the distribution of variouscharacter states of angiosperms.• Superorder rank result in a realistic arrangement offamilies and orders.
Drawbacks• The system covers only flowering plants.• Does not proceed below the family level, not useful forarranging specimens in herbarium.• Based mostly on morphological & chemical characters.• Recent molecular studies justified the placement ofsome families.