Rolf M.T. Dahlgren

1932-1987

Professor of botany in University of Copenhagen.

Published his original version of his system in 1975.

Most notable classification system in the resent history.

Major interest= evolutionary characters within the angiosperms(class Magnoliopsida)

Used a two dimensional graphic system(Dahlgrenogram/bubble diagrams) to display his phylogenetic system.

Dahlgren himself was much interested in phylogeny.

Mostly morphological and phytochemical characters considered.

Used the “-iflorae” endings in his superorders.

Characters concidered.. Apocarpy,syncarpy & monocarpy conditions

Choripetaly,sympetaly & mono-aperaturate pollen types

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 a

phylogenetic tree.

Groups are represented by bubbles of different sizes between which relationships are implied-though not clearly shown.

Much used to display results of broad surveys of variation of characters.eg- the types of plastids in the sieve tubes

More closely related to Bessey’s cactus-like diagram

Angiosperms (class Magnoliopsida/ class Angiospermae)

subclass-Magnolideae subclass-Lillidae

-represent dicotyledons -represent monocotyledons

24 super orders 07 super orders

80 orders 26 orders

346 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 various character states of angiosperms.

• Superorder rank result in a realistic arrangement of families and orders.

Drawbacks

• The system covers only flowering plants.

• Does not proceed below the family level, not useful for arranging specimens in herbarium.

• Based mostly on morphological & chemical characters.

• Recent molecular studies justified the placement of some families.

References Walters.D.R, Keil.D.J, Murrell Z.E, Vascular plant

taxonomy, 5th edition ,page 105-109,Kendall/Hunt publishing company, Lowa,USA

Jones.S.B, Luchsinger.A.E, Plant systematics, 2nd

edition,McGraw-Hill, Inc. NY .page 144-147

http://www.jstor.org/pss/3667872 (02.02.2012)