80 ĐỀ THI THỬ TUYỂN SINH TIẾNG ANH VÀO 10 SỞ GD – ĐT THÀNH PHỐ HỒ CHÍ MINH NĂ...
Dahlgren’s system
1.
2.
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
7.
8.
9.
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.
