Dahlgren’s system

1,555 views
1,182 views

Published on

Published in: Education, Technology
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,555
On SlideShare
0
From Embeds
0
Number of Embeds
5
Actions
Shares
0
Downloads
14
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Dahlgren’s system

  1. 1.  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.
  2. 2.  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.
  3. 3. 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.
  4. 4. 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
  5. 5. Angiosperms (class Magnoliopsida/class Angiospermae)subclass-Magnolideae subclass-Lillidae-represent dicotyledons -represent monocotyledons24 super orders 07 super orders80 orders 26 orders346 families 92 families
  6. 6. 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.
  7. 7. 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.
  8. 8. References Walters.D.R, Keil.D.J, Murrell Z.E, Vascular planttaxonomy, 5th edition ,page 105-109,Kendall/Huntpublishing company, Lowa,USA Jones.S.B, Luchsinger.A.E, Plant systematics, 2ndedition,McGraw-Hill, Inc. NY .page 144-147 http://www.jstor.org/pss/3667872 (02.02.2012)

×