Rolf Dahlgren was a Danish botanist who published an influential plant classification system in 1975. He used a two-dimensional graphic system called a Dahlgrenogram to display phylogenetic relationships among plant groups. Dahlgren's system was based primarily on morphological and chemical characteristics and divided angiosperms into 31 superorders within two subclasses. While comprehensive, it considered only flowering plants and did not classify below the family level. Subsequent molecular studies have revised placements of some families from Dahlgren's system.

3.  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.

4.  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.

5. 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.

6. 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

10. 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

11. 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.

12. 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.

13. 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)