Taxonomy
of Flowering Plants - LECTURE
NOTES
Hugh
D.
Wilson
The Rosidae
The Subclass Dilleniidae, includes 18 orders, 116
families
and over 60,000 species. The largest subclass with regard to
number
of families and comparable to the Asteridae with regard to species
diversity.
As was the case with the Dilleniidae, about 75% of the species occur in
five orders; in this case the Fabales (18,000),
Myrtales
(9,000), Euphorbiales (8,000), Rosales (6,600) and Sapindales
(5,400).
Also, local Santalales
- Rafflesiales
(Phoradendron
- Viscaceae).
A diverse set of flowering
plant
orders that, like the Dilleniidae, lacks a distinct set of key
characters.
General trends or features of the Subclass include:
- syncarpy is the rule,
with
the exception
of the high frequency of apocarpy in the Rosales and monocarpy
in
the Fabales and Proteales.
- Leaves are often simple
or,
if compound,
often pinnately compound
- petals usually distinct,
sometimes
wanting, sometimes connate at the base, rarely sympetalous.
- nectary disks of various
types are
frequently encountered, many stamodial in origin and positioned at the
base of the ovary.
- placentation is
various, but
most often axile with, generally, fewer ovules per locule than found in
the Dilleniidae.
Cronquist: "In the last analysis, the Rosidae
and
Dilleniidae
are kept apart as subclasses because each seems to constitute a natural
group separately derived from the ancestral Magnoliidae, rather
than because of any definitive distinguishing characters...it is
conceptually
more useful to hold the two as separate subclasses than to combine them
into one or to abandon any attempt at organization of the Magnoliopsida
into subclasses." THEREFORE: Focus here is on
distinctive
characters at the order and family level.
Our coverage of the Rosidae will include:
Rosales
Crassulaceae
Rosaceae
Fabales
(Leguminosae)
Mimosaceae
Caesalpiniaceae
Fabaceae
Myrtales
Onagraceae
Euphorbiales
Euphorbiaceae
Apiales
Apiaceae
(Umbelliferae)
Return to Lecture
Notes, the Biology
301 homepage, the Asteridae,
or
the Dilleniidae