ORIGIN AND CLASSIFICATION OF ANGIOSPERMS

Jenny Xiang xianjenn at ISU.EDU
Mon Jan 4 17:15:30 CST 1999


Dear Taxonomists,

For those who are interested in the origin and classification of
angiosperms, here are two recent papers proposing a new hypothesis and a
new classification scheme.  Below are the abstracts of these papers.

 (5): 385 - 402 (1998)   Acta Phytotaxonomica Sinica

ON PRIMARY SUBDIVISIONS OF THE MAGNOLIOPHYTA TOWARDS A NEW SCHEME FOR AN
EIGHT-CLASS SYSTEM OF CLASSIFICATION OF THE ANGIOSPERMS

2WU Zheng-Yi
 1TALNG Yan-Cheng
1LU An-Ming
1CHEN Zhi-Duan

1Labomtory of Systematic and Evolutionary Botanv, Institute of Botany,
the Chinese Academy of Sciences, Beijing 100093)

2Kunming Institute of Botany, the ChineseAcadmy of Sciences, Kunming
650204)

Abstract - The current subdivision of the anglosperrm into two major
groups, the dicotyledons and the monocotyledons, whether at the rank of
class or subclass, is greatly challenged by more and more evidence from
comparative morphology, chemotaxonomv, paleobotany, cladistics and
molecular systematics.  It becomes clear that this primary subdivision
is conventional rather than natural.  We stressed in this paper that the
system of classification of the angiosperms should be as much as
possible based on the geneaological relationships of major groups.  It
seems apparent that eight principal lineages appeared by the end of the
Eariv Cretaceous when the one of the major radiation of the angiosperms
occurred.  By using the Linnean hierarchy, these lineages are named at
the rank of class in order to reflect major evolutionary trends within
the anglosper-ms.  As evolutionary syste=3Dtists, we accepted
'paraphyletic' groups as natural in this scheme.  The eight classes are
as follows:

Magnoliopsida (including Degeneriaceae, Himantandraceae, Magnollaceae,
Winteraceae, Canellaceae, Illiciaceae, Schisandraceae,
Austrobailevaceae, Eupomatiaceae, Annonaceae, Myristicaceae,
Hydropeltidaceae, Cabombaceae, Nupharaceae, Nymphaeaceae, Barclayaceae,
Ceratophyllaceae,

Lauropsida ( including Amborellaceae, Trimeniaceae, Monimiaceae,
Gomortegaceae, Hemandiacea'e, Lauraceae, Calycanthaceae,
Idiospem-iaceae, Chloranthaceae),

Piperopsida ( including Aristolochiaceae, Saururaceae, Piperaceae,
Lactoridaceae ),

Caryophyllopsida ( including Caryophyllaceae, Molluginaceae, Aizoaceae,
Amaranthaceae, Chenopodiaceae, Halophytaceae, Stegnospermataceae,
Achatocarpaceae, Phytolacaceae, Nyctaginaceae, Cactaceae, Portulacaceae,
Didiereaceae, Basellaceae, Hectorellaceae)
Liliopsida (including the families of Liliopsida sensu Takhtajan(1997),

Ranunculopsida (including Ranunculaceae, Lardizabalaceae,
Sargentodoxaceae, Menispermaceae, Circaeasteraceae, Nandinaceae,
Berberidaceae (incl.  Ranzaniaceae), Leonticaceae, PodophyUaceae,
Hvdrastidaceae, Glaucidiaceae, Paeonlaceae, Pteridophyllaceae,
Papaveraceae, Hypecoaceae, Fumariadeae, Nelumbonaceae),

Hamanelidopsida (including Trochcdendraceae, Tetracentraceae,
Cercidiphyllaceae, Eupteleaceae, Myrothamnaceae, Hamamelidaceae,
Planaceae), and

Rosopsida (including the families of Rafflesianae, Balanophoranae,
Hamamelididae p.p., Dilleniidae, Rosidae, Cornidae, Lamiidae, Asteridae
sensu Takhtajan (1977).  Principal families in each class are discussed
here.  Further study is needed to elucidate the phylogenetic
relatinships among and within the classes.


************************************************************************

ProceedIngs of the IFCD (1996),269-334.

  A COMPREHENSIVE STUDY OF =93MAGNOLIIDAE=94
SENSU LATO -WITH SPECIAL CONSIDERATION
ON THE POSSIBILITY AND THE NECESSITY FOR PROPOSING A NEW
=93POLYPHYLETIC-POLYCHRONIC-POLYTOPIC=94 SYSTEM OF ANGIOSPERMS


Wu Zhengyi

Kunming Institute of Botany, Chinese Academy of Science,, Kun ing
650204,P.  R. China

Lu Annin, Tang Yancheng
Institute of Botany, Chinese Academy of Sciences, Beijing 100093,P.  R.
China

ABSTRACT. A comprehensive study f "Magnoijidae" sensu lato was made
(following Takhtajan system with some families eliminated, including
about 50 families).  They are rearranged into 15 evolutionary stocks, 24
orders and 45 families according to the proposed new
"Polyphyletic-Polychronic-Polytopic=94 idea, mainly based on the study of
time of origin and birthplaces of the taxa studied by a
multidisciplinary approach.  The emergence of most of the studied
families could have been on different continental plates of "Pangaea" in
some of the latest two platetectonic assemblages of "Pangaea ". Our
"Polyphyletic " is not "artificial ", but something of
poly-(mono)phyletic during the time Of explosion, in other words, the
explo I' of many monophyletic groups after mass extinction of ancient
lineages.  Following such a hypotsheosnis, it is not difficult to
urnmarize the Present debate between the phyletic gradualism and the pu
nctuated equilibrium in the field of paleontology.  Eventually, a
concept of Tri-diMensional Rhythmic Evolution may be roposed.

Key words      A comprehesive study Of Magnoliidae sezisu lato;
Polyphyletic-Polychronic-polytopic system; Tri-dirnensiorial Rhythmic
Evolution

ForeWord
When studying the origin of the Chinese seed Plant flora, we are
inevitably faced with the problem of the origin of the seed plants as a
whole: the time, place, manner of origin and the process of
differentiation.  Research on 56 families (or genera), mostly
angiosperms, is a subproject of the Floristic Geography of the Chinese
Seed Plants, a key note project sponsored by the Natural Science
Foundation of China.  An overview of the results of the sub-project
indicates that the time of origin, of the angiosperms could be dated
back to the Early Jurassic, I!en to the Late Triassic.  In the taxa that
have been studied, there are both north to south and west to east
vicariant (or long distance dispersed) families, genera and species.
This causes us to ssume that the emergence of most of the studied
families could have been on different continental plates of "pangaea"
sometimes between the latest two plate-tectonic assemblages of
"pangaea". Evidence from paleogeography geology, stratigraphy and
palaentology, as reported by Shields (1979), Sepkoski (1989) and Wang et
al. (1997, in Chinese) , reveals that there a catastrophic extinctions
in the history of the life on the earth. Among these, the late Triassic
and the late Cretaceous could have been the two major opportunities for
the origin and explosion of the angiosperms. During the late Triassic,
at least the ancient forms of the angiosperms (the  proto-anglosperms )
had already rapidly diversified following the mass extinction of their
ancestors. These have evolved into the ancient forms of different clades
or phyleses of the extant Angiosperms. Some of those extant anglosperms
are still continuing to differentiate.  Therefore, the explosive
emergence of angiosperms in the early Cretaceous, from primitive to
advanced groups, may no longer be the 'mystery' that was pointed out by
Darwin. Furthermore, the disjunct distribution of some primitive
families or genera on different continents, separated by oceans, can be
more reasonably and logically explained. Accordingly, we assume that
Angiosperms have experienced an evolutionary history of 200(-250)
million years (some at least).  Many ancient forms became extinct. Only
a few of these plants were fossilized and not many of their fossils have
been discovered. In this situation, from the point of view of
florogenesis, a system of classification of angiosperms can only be
arranged in the form of a cross-section diagram, like the
"Dahlgrenogram=94, which was used by R. Dahlgren and R. Thorne, even
though there exist many very isolated and very ancient relicts in the
angiosperms. These could be the major facts of angiosperm evolution.
Some taxa may have originated in a monopliyletic-monochronic-polytopic
manner, but in most circumstances, the Angiosperms may have a
polyphyletic-polychronic-polytopic origin. However, when we trace back
to the ancestors of the proto-angiosperms, they still have a unitary
origin. Those ancestors also have originated from an internally widely
differentiated ancient group. We suspect that it could be
"polyphyletic", but not =93artificial" in the sense of Wiley et al.
(1991). This is something of poly(-mono)-phyletic during the time of
explosion, in other words, the explosion of many monophylet' groups
after mass extinction of ancient lineages. Following such a hypothesis,
it is not difficult to summarize the present debate between the phyletic
gradualism and the punctuated equilibrium in the field of palaeontology,
into the fact of transformation of gradual changes and sudden changes,
the two contradictory aspects within a thing. Eventually, a concept of
Tri-dimensional Rhythmic Evolution may be proposed. This concept
correlates with a point recently made in the field of geology and
palaeontology in China, which summarize that the evolution of the earth
and its organisms is a process of interchange between long-time and slow
gradual changes versus short-time and rapid sudden changes. The two
fields of study verify each other. This point of view is in fact from
another important angle supported by the evidence of the polyphyly of
Ainglosperm flowers (Les et al. , 1996).

Jenny Xiang




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