全 文 ：Received 13 Jan. 2003 Accepted 19 Aug. 2003
Supported by the National Natural Science Foundation of China (39770045).
http://www.chineseplantscience.com
Ultrastructure of Pollen Exine in Peucedaneae Drude with Reference to
Its Systematic Significance
SHU Pu, SHEH Meng-Lan
(Nanjing Botanical Garden Mem. Sun Yat-Sen, Institute of Botany, Jiangsu Province and The Chinese
Academy of Sciences, Nanjing 210014, China)
Abstract: Transmission electron microscopy (TEM) observation of pollen grains of 18 species belonging
to 18 respective genera of the tribe Peucedaneae Drude revealed distinct ultrastructural difference in the
pollen exine, including the thickness and features of tectum, columnar layer, foot layer and endexine. The
systematic position of those 18 species are re-evaluated based on their ultrastructural characteristics of
pollen exine observed in this study. Seven genera related to Angelica L. in Angelicinae Drude have been
deduced to genus Angelica L. For example, Ostericum grosseserratum (Maxim.) Kitagawa was changed to
Angelica L. by some authors, but it differs from Angelica sinensis (Oliv.) Diels in having well developed
tectum which is thicker than the columnar layer and foot layer. Its columnar layer is quite well-developed
with long and branched columellae. Besides its surface is tuberculated. Evidently, its development exceeds
that of Angelica sinensis. However, it is only a moderate evolutional species in its genus, and the Angelica
sinensis accounts as the most advanced species in Angelica Diels, thus, placing genus Ostericum Hoffm.
in Angelica L. is not suitable, it may be more appropriate to keep its original position. In addition, Ferula
akitschkensis B. Fedtsch. ex K.-Pol. differs greatly from those of Talassia transiliensis (Herd.) Korov. and
Schumannia turcomnnia Kuntze, because of its very well-developed columnar layer, being about four to
five times thicker than the total of tectum and foot layer, tuberculated tectum surface and complicated
structure of columnellae. As another species Heracleum forrestii Wolff also differs from Semenovia rubtzovii
(Schischk.) Monden. in having an even thickness of exine and well-developed columnar layer, it seems
suitable that they should also be treated as two independent genera.
Key words: Peucedaneae Drude; pollen exine; ultrastructure; systematic position
Peucedaneae is a large tribe in Umbelliferae. The sys-
tematic positions of some satellite genera of Ostericum
Hoffm., Czernaevia Turcz., Conioselinum Fisch. ex Hoffm.,
Coelopleurum Ledeb. in the subtribe of Angelicinae Drude,
Schumannia Kuntze and Talassia Korov. in the subtribe of
Ferulinae Drude, and Semnovia Regel et Herd. in the
subtribe of Tordyliinae Drude are unsettled. Some opinion
preferred that these genera would be valid and other opin-
ion suggested that they would be treated together with
Angelica L., Ferula L. or Heracleum L. respectively. Study-
ing the structure of pollen exine and other relevant charac-
teristics in association with evolution may provide an im-
portant systematic basis for classification. The present
study involves the structural observation of pollen grains
in different representative species of genera in Peucedaneae
in an attempt to attack the existing systematic problems.
According to the system proposed by Shan and Sheh
(1992), 20 genera in Peucedaneae Drude are listed sepa-
rately under Angelicinae Drude, Ferulinae Drude, and
Tordyliinae Drude. In the present study, pollen grains were
collected from 18 individual species of 18 genera, each as
representative species of the respective genus, for ultra-
structural observation. Due to the limited specimens, obser-
vation of Soranthus Ledeb. of Ferulinae Drude and
Tetrataenium (DC.) Manden. of Tordyllinae Drude were not
included.
1 Materials and Methods
Most of the pollen grains were collected from our
herbarium, and the rest were collected from fields, they are
Chuanminshen violaceum Sheh et Shan, Ostericum
grosseserratum (Maxim.) Kitagawa, Glehnia littoralis Fr.
Schmidt ex Miq., Levisticum officinale Koch, and Pastinaca
sativa L., and few from the Herbarium of Xinjiang Biological
Soil and Desert Institute, they are Talassia transiliensis
(Herd.) Korov. and Schumannia turcomanica Kuntze. The
specimens were fixed with 2% osmic acid for 48 h, dehy-
drated through a graded series or alcohol, finally embed-
ded in Epon 812 and spurs for two to three days. Polymer-
ization was carried out in a vacuum oven at 55-60 ℃. Ultra-
thin sections were cut with an LKB-8800 microtome, and
sections were treated with uranium acetate peroxide for two
Acta Botanica Sinica
植 物 学 报 2004, 46 (3): 311-318
Acta Botanica Sinica 植物学报 Vol.46 No.3 2004312
hours. Specimens were examined and photographed un-
der an electron microscope.
2 Observation and Results
2.1 Angelicinae Drude
2.1.1 Conioselinum chinense (L.) Britton, Sterns et
Poggenburg (Fig.1, E, I) Tectum is rather thin, with the
same thickness as foot layer. The polar area is rather flat,
the surface of the equatorial area is irregularly wavy, and
possesses small number of tuberculates. Columnar layer is
rather thick with columellae rather long and wide. Columel-
lae at sub-polar area and equatorial area were short, small
and thick, being well developed. Endexine is thin, increases
in thickness at the pore. Intine is thin with protrusion.
2.1.2 Archangelica brevicaulis (Rupr.) Rchb. (Fig.1, O,
R) The tectum at the polar area is rather thick，but is
thin at equatorial area. Surface is wavy. Columellae at the
polar area are rather long and thick, while short, thickly
arranged, and well developed at equatorial area. Foot layer
is rather thin. Endexine as well as intine is thin with increas-
ing thickness towards the pore and protruded into contour
lines.
2.1.3 Coelopleurum nakaianum (Kitagawa) Kitagawa
(Fig.1M) Tectum, columnar layer and foot layer are all
very thick, with almost the same thickness. The foot layer
is thicker than tectum at the polar area. The thickness of
columnar layer is unevenly distributed, being thick between
the colpi and very thin near the colpus. The columellae, not
well developed, become smaller, and dot-like densely ar-
ranged near the pore. Similar uneven thickness was also
found with endexine. Intine is very thin, with evidently in-
creased thickness near the pore and it is raised and pro-
truded into contour lines.
2.1.4 Czernaevia laevigata Turcz. (Fig.1K) Tectum is
rather thick, and surface is slightly wavy near the colpus.
Columnar layer is very thin, being 1/3-1/2 of tectum. Col-
umellae are poorly developed being short bar to dot-like in
shape. Foot layer is as thick as tectum. Endexine is thin but
increases its thickness and is raised at the pore.
2.1.5 Angelica sinensis (Oliv.) Diels (Fig.3S) The
tectum is thicker than foot layer with small tumorous
protuberances. Columnar layer is rather thick at the space
between the colpi becoming very thin near the colpus. Col-
umellae are thick with various lengths. Foot layer is thinner
than tectum. Endexine is thin and increases in thickness at
both sides of colpus. Intine increases its thickness at the
pore.
2.1.6 Ostericum grosseserratum (Maxim.) Kitagawa (Fig.
1, B, F) Tectum possesses the same thickness as the foot
layer, while columnar layer is thicker. Columellae are rather
long, and even in appearance and are regularly arranged
and well developed. Columellae are shorter and densely
arranged at the equatorial area. Foot layer is thin. Endexine
is thick, with increased thickness towards the pore. Intine
is very thin, with the thick part at the pore.
2.1.7 Levisticum officinale Koch (Fig.1W) Tectum
increases its thickness at the polar area forming a lap, which
is two to three times the thickness of tectum at the equato-
rial area, whereas the tectum is very thin with even wavy
surface. The columnar layer is unevenly thickened at polar
area and very thin at equatorial area. The columellae are
small, long, regularly arranged and well developed. Foot
layer is thinner than tectum and uneven. Endexine is thin
and even, and becomes thicker at the pore. Intine is thin,
but becomes much more thicker and protruded at the pore.
2.1.8 Glehnia littoralis Fr. Schmidt ex Miq. (Fig.1V) Tec-
tum is rather thick as thick as the foot layer. Its surface is
slightly wavy at the equatorial area. Columnar layer is
slightly thicker than, if not the same as, the foot layer. Col-
umellae at the polar area is short and thick, being regularly
arranged or few and scattered, however at equatorial area it
is short and small with variation in form and size, and is
unevenly developed.
2.2 Ferulinae Drude
2.2.1 Arcuatopterus filipedicellus Sheh et Shan (Fig.1,
G) Tectum is thicker than foot layer and sustains its
thickness at colpus and the space between the colpi, and
the surface is uneven possessing hairy protuberances. Co-
lumnar layer is thinner than tectum, and columellae are short
with different shapes and sizes and not well developed.
Foot layer is thinner than tectum and slightly thicker at
interspaces of colpi. Endexine is thin in spaces between
colpi and very thin at intine, but greatly thickened at pore,
protrudes at contour.
2.2.2 Ferula akitschkensis B. Fedtsch. ex K.-Pol. (Fig.1,
X,Y) Both tectum and foot layer are thin and equal in
thickness, with small tumorous protuberances on the
surface. Columnar layer is very thick about four to five
times as thick as the tectum. Columellae are long and thick
with finger-like branches or without definite shape at polar
area, and short and densely arranged at sub-polar area, and
small and evenly arranged near pore. Endexine is very thin
at polar area, but increases thickness near the pore and is
mostly thickened near the pore margin, then abruptly turns
thin and finally disappears. Intine is not obvious, but
strongly increases its thickness and protrudes at the
contour.
2.2.3 Schumannia turcomanica Kuntze (Fig.1J) Tectum
313SHU Pu et al.: Ultrastructure of Pollen Exine in Peucedaneae Drude with Reference to Its Systematic Significance
Fig.1. Ultrastructure of pollen exine in different groups of Peucedaneae Drude. A. Semenovia rubtzovii. Polar view, showing thickened
tectum at the polar area, and with small round pellet-like protuberances on the surface, ×6 000. B, F. Ostericum grosseserratum. Polar
view, showing exine structure at polar area and mesocolpus, both tectum and foot layer are thin, while columnar layer is thicker. B.
×6 000. F.×8 000. C, H. Heracleum forrestii. Polar view, showing exine structure at polar area and mesocolpus, tectum, columnar layer
and foot layer possess the same thickness with shallow wavy surface and hillock-like protuberances. C.×4 000. H.×8 000. D. Talassia
transiliensis. Equatorial view, showing thin tectum, and with small tumorous protuberances on the surface, ×3 500. E, I. Conioselinum
chinense. A part of equatorial view, showing thinner tectum, irregularly wavy surface and possesses small number of tuberculates. E.
×5 000. I. ×8 000. G. Arcuatopterus filipedicellus. Polar view, showing exine structure at polar area and mesocolpus, tectum thicker
than foot layer, and sustains its thickness at colpus and the space between the colpi, × 6 000.
Acta Botanica Sinica 植物学报 Vol.46 No.3 2004314
Fig.1. Ultrastructure of pollen exine in different groups of Peucedaneae Drude. J. Schumannia turcomanica. A part of equatorial view,
showing tectum slightly thicker than foot layer, surface uneven at equatorial area, and with small tumorous protuberances, ×4 000. K.
Czernaevia laevigata. A part of equatorial view, showing rather thick tectum, slightly wavy on the surface near colpus, ×6 000. L, P.
Pastinaca sativa. Equatorial view, showing very thick sexine, about three times the thickness of endexine. L.×3 000. P.×8 000. M.
Coelopleurum nakaianum. Equatorial view, showing tectum, columnar layer and foot layer are all very thick and almost the same
thickness, the columellae not well developed, ×5 000. N, Q. Phlojodicarpus villosus. A part of equatorial view, showing rather thick
tectum and thin columnar layer, especially thin at equatorial area. N.× 6 000. Q.× 10 000. O, R. Archangelica brevicaulis. A part of
equatorial view, showing rather thick tectum at the polar area, but thinner at equatorial area, surface slightly wavy. O.×3 500. R.×6 000.
315SHU Pu et al.: Ultrastructure of Pollen Exine in Peucedaneae Drude with Reference to Its Systematic Significance
Fig.1. Ultrastructure of pollen exine in different groups of Peucedaneae Drude. S. Angelica sinensis. Polar view, showing the thickness
of tectum uneven and with small tumorous protuberances on the surface, tectum thicker than foot layer, ×6 000. T, U. Chuaminshen
violaceum. Equatorial view, showing rather thick tectum, with shallow wavy surface and small tumorous protuberances. T.×6 000. U.
×10 000. V. Glehnia littoralis. Equatorial view, showing rather thick tectum, protrude as thick as foot layer, ×6 000. W. Levisticum
officinale. Polar view, showing intensely thickened tectum forming a lap at the polar area, but very thin at equatorial area, ×4 000. X, Y.
Ferula akitschkensis. Transverse section of exine and polar view, showing both tectum and foot layer thin and equally in thickness, with
small tumorous protuberances on the surface. X.×4 000. Y.×8 000. Z, a. Peucedanum turgeniifolium. Transverse section of exine and
part of exine view, showing very thick tectum at the polar area and gradually becomes thinned towards colpus, surface uneven with
hillock-like protuberances. Z.×5 000. a.×8 000.
Acta Botanica Sinica 植物学报 Vol.46 No.3 2004316
is somewhat thicker than or as thin as the foot layer. The
surface at equatorial area is uneven with full of humps and
holes, and some small tumorous protuberances, with even
thickness of exine. Columnar layer is rather thin. Columel-
lae are thick and very short. They are small, dot-like and
regularly arranged at equatorial area. Foot layer is rather
thin. Endexine is not evenly thickened, being thickened
near the colpus region. Intine is not distinct. Its thickness
is sharply increased being protruded at the pore.
2.2.4 Phlojodicarpus villosus (Turcz. ex Fisch. et Mey.)
Turcz. ex Ledeb. (Fig.1, N, Q) Tectum is rather thick, its
surface is rather flat at the polar area and wavy at the equa-
torial area. Columnar layer is thin, especially at the equato-
rial area. Columellae are thick, short and small and of vari-
ous shapes. They are densely arranged and not well
developed. Both foot layer and endexine are very thin, but
increase in thickness at the polar area. Intine is thin and
distinct at the pore.
2.2.5 Peucedanum turgeniifolium Wolff (Fig.1, Z, a)
Tectum is very thick at the polar area and gradually be-
comes thinned towards colpus. Surface is uneven with hill-
ock-like protuberances. Columnar layer is thick but slightly
thinner than tectum. Columellae are wavy in shape, being
segmented and bifurcated and becoming smaller and ag-
gregated towards the pore. Foot layer is thin, even and
distinct. Endexine is very thick, with increasing thickness
and protruding at the pore.
2.2.6 Chuanminshen violaceum Sheh et Shan (Fig.1, T,
U) Tectum is rather thick, with shallow wavy surface and
small tumorous protuberances. Columnar layer is the same
as or thicker than foot layer. Columellae with different
shapes, are short, branched, and packedly arranged near
the pore. Foot layer is rather thin, with even thickness.
Endexine is thin, evident and increases its thickness at the
pore. Intine is thin, but evidently increases in thickness at
the pore.
2.2.7 Talassia transiliensis (Herd.) Korov. (Fig.1D) Tec-
tum is evenly as thin as the columnar layer. It is even at the
polar area, but with small tumorous protuberances at the
equatorial area. Columellae are tubular in shape, regularly
arranged, rather packed near the pore, and well developed.
Foot layer is very thin, irregular, sometimes not evident.
Endexine is thin with increasing thickness near the pore.
Intine evidently increases its thickness at the pore, show-
ing protrusions at contour.
2.3 Tordyliinae Drude
2.3.1 Pastinaca sativa L. (Fig.1, L, P) Sexine is very
thick, about three times the thickness of endexine. Tectum
is rather thick, having a flat surface. Columnar layer is thin,
and not well differentiated. Columellae, having no definite
shape, are in the process of forming a typical columnar
layer. Foot layer is thinner than tectum, but apparently thick-
ened at the equatorial area. Endexine is thin, but thickened
at the pore. Intine is thickened at the pore, but not raised.
2.3.2 Semenovia rubtzovii (Schischk.) Manden. (Fig.1
A) Tectum is thin, but is only thickened at the polar area.
It has small round pellet-like protuberances on the surface
at the pore. Columnar layer is very thick and columellae are
long at mesocolpus. However, columnar layer becomes
thinned, columellae become short and densely arranged at
colpus area. Foot layer is very thin, so with endexine evi-
dently increases the thickness near the pore. Intine is not
evident, and increases its thickness at the pore.
2.3.3 Heracleum forrestii Wolff (Fig.1, C, H) Tectum,
columnar layer and foot layer share the same thickness
with flat and shallow wavy surface and hillock-like
protuberances. The columnar layer is evenly thickened, well
developed, containing regular, evenly dense columellae that
become small, pointed and densely packed at the pore. Foot
layer is evenly thickened and regular. Endexine is rather
thin, and increases its thickness towards the pore, but along
with the sexine, they disappear at the pore. Intine is very
thin, and becomes rather thick and raised near the pore.
3 Discussion and Conclusion
According to the Drude Classification System,
Peucedaneae Drude is divided into three subtribes, namely
Angelicinae Drude, Ferulinae Drude and Tordyliinae Drude
(Drude, 1898). Based on the ultrastructural study of pollen
grains of the 18 species in China belonging to 18 genera of
Peucedaneae Drude, the systematic position of these spe-
cies are discussed as follows.
3.1 Angelicinae Drude
Eight genera of this subtribe are found in China, the
classification of which is world-wide debatable. The North
American and European scholars tend to embody all under
Angelica Drude in a broad sense. In the North American
Flora (Mathias and Constance, 1944) Ostericum Hoffm.,
Coelopleurum Ledeb. and Czernaevia Turcz. are put un-
der Angelicinae Drude. In the European Flora (Tutin and
Heywood, 1968) Coelopleurum Ledeb. and Archangelica
Hoffm, which are distributed in Europe, are included under
Angelica Drude. Hiroe and Constance (1965), also put
Ostericum Hoffm., Coelopleurum Ledeb. and Archangelica
Hoffm. in Angelica Durde. In Flora USSR (Schischk, 1951),
Schischk only put Czernaevia Turcz. under Angelica Drude,
and left the other genera in their own position. In Flora
Reipublicae Popularis Sinicae (Shan and Sheh, 1992)
317SHU Pu et al.: Ultrastructure of Pollen Exine in Peucedaneae Drude with Reference to Its Systematic Significance
Angelica Drude and its relative genera are all treated as
independent genera.
Based on the ultrastructural observation of pollen grains,
differences in degree among the genera do exist. The com-
mon features of the representative species of these eight
genera are that they all have complete exine (including sexine
and endexine) and intine. The exine contains the tectum,
columnar layer and foot layer, and the endexine is very thin
and distinct and intine is also very thin.
Concerning the relation of Angelica Drude to several
other neighborhood genera, striking difference was found
between Ostericum Hoff. and Angelica Drude. Take
Ostericum grosseserratum for instance, its tectum with well
developed tumorous protuberances has similar thickness
as that of foot layer but thicker than intine. The well devel-
oped columnar layer is thicker than that of tectum and foot
layer with long forked and regularly arranged columellae as
well as the thick endexine. All these characteristics showed
an advanced level in species evolution. In comparison, al-
though the tectum of Angelica sinensis also possesses
tumorous protuberances, yet its columnar layer is not well
developed and does not form typical columnar structure.
Referring to pollen morphology, Angelica sinensis is ac-
counted as the most advanced species in Angelica Drude
(Shu and Sheh, 2001), whereas Ostericum grosseserratum
is only considered at a moderate evolutional level in
Ostericum, which is higher than that of Angelica Drude.
Thus we may infer that the evolutional level of Ostericum
grosseserratum is much higher than and should be distin-
guished from Angelica Drude and it should have its own
independent position.
Other characteristic features should also be mentioned.
For example, the columellae in Archangelica brevicaulis
are even in size, regularly arranged, and well developed. In
Coelopleurum nakaianum, all tectum, columnar layer and
foot layer are very thick, having the same thickness, and
columellae have different shapes and sizes and are not well
developed. In Czernaevia laevigata columnar layer is par-
ticularly thin, being 1/3-1/2 the thickness of tectum. Col-
umellae are poorly developed. In Levisticum officinale tec-
tum increases its thickness and appearance at the polar
area, but is very thin at the equatorial area, and columnar
layer is well developed. In Conioselinum chinense tectum
is thin, but columnar layer is thick and well developed. In
Glehnia littoralis tectum and foot layer show a similar
thickness, and columnar layer is thicker than foot layer,
and columellae are well developed at polar area, but not so
well developed at equatorial area. The above description
demonstrates clearly the individual characteristic differences
of pollen grain structure among the genera, especially the
single genus Czernaevia Turcz. and the small genera
Glehnia Fr. Schmidt ex Miq. and Levisticum Hill. The obvi-
ous difference of these species offers a strong evidence to
the position of their genera and to their subtribe
classification. Thus, based on the above viewpoint, we pro-
pose the following sequential order of Angelicinae Drude:
Ostericum grosseserratum→Archangelica brevicaulis→
Levisticum officinale→ Conioselinum chinense→
Glehnia littoralis→ Angelica sinensis → Czernaevia
laevigata → Coelopleurum nakaianum.
3.2 Ferulinae Drude
The systematic position of this subtribe with the eight
genera from China remained controversal. Schumannia
Kuntze, established by Kuntze (1887) has been widely
adopted. In 1980, Pimenov (1980) put it in Ferula L. be-
cause of the presence of hardened cells in the fruit epidermis.
There are three different opinions as regard to the position
of Talassia Korov. At first it was recognized as a member of
Peucedanum L. In 1963, Korovin (1963) established a new
genus for it. In 1983, Pimenov (1983) transferred it back to
Ferula L. because of the anatomical characteristics of fruit.
Phlojodicarpus Turcz. ex Bess. was also put in Peucedanun
L. Besides, Soranthus Ledeb. was also recognized as a mem-
ber of Ferula L. because of the lack of pollen specimen, it
was not evaluated.
As for the pollen exine ultrastructure of Talassia Korov.,
the tectum, columnar layer and foot layer are all very thin,
the former two layers being evenly thick, with small tumor-
ous protuberances on the surface, and columellae are ar-
ranged regularly, but poorly developed. Although the tec-
tum is thin, the columnar layer is about four to five times
thicker than tectum and foot layer with complicated
columellae. However, Peucedanum turgeniifolium is quite
different from the former two, by its very thick tectum and
thick endexine. Therefore, Talassia transiliensis is differ-
ent from Ferula akitschkensis as well as from Peucedanum
turgeniifolium. Especially with its exine structure being
rather specific, treating it as an independent genus is more
appropriate.
The ultrastructure of exine in Schumannia turcomanica
is definitely different from that of Ferula akitschkensis
because of its thickened tectum, higher number of tumor-
ous protuberance on the surface, thinner columnar layer
and less well developed columellae. Besides, the
Phlojodicarpus villosus differs from Peucedanum
turgeniifolium, in that the endexine is exceedingly thin,
with uniform thickness, being only as thick as 1/5-1/6 of
sexine. The endexine of Peucedanum turgeniifolium is very
Acta Botanica Sinica 植物学报 Vol.46 No.3 2004318
thick, and the thickness is uneven, while its sexine is only
1/2 or the same as endexine in thickness. Judged from these
characteristics, they should not be treated as in one group.
The developmental pattern of exine represents the de-
gree of evolution of the different groups. Generally speaking,
the thickness of extine, as well as the columnar layer,
evolves from thin to thick as pollen evolution advance from
primitive to advanced group, so with the change in colum-
nar layer. According to the observation of seven genera
(species) of Ferulinae Drude, the evolution trend is pro-
posed as: Ferula akitschkensis→ Peucedanum
t u r g e n i i f o l i u m → P h l o j o d i c a r p u s v i l l o s u s →
Chuanminshen violaceum→ Talassia transiliensis→
Schumannia turcomanica→Arcuatopterus filipedicellus.
3.3 Tordyliinae Drude
The systematic classification of this subtribe including
four genera from China also exists different opinions. For
instance, Semenovia Regel et Herd. and Tetrataenium (DC.)
Manden. are combined as Heracleum L. since material
Tetrataenium (DC.) Manden. has not been studied. In
Semenovia rubtzovii, its tectum surface possesses small
pellet-like structure, with small and short cilia at the pore,
the columnar layer is unevenly thickened with different sizes
and shapes. The degree of evolution is not as advanced as
Heracleum forrestii. In Heracleum forrestii tectum surface
is slightly wavy, with small number of small hill-like
protuberances, the thickness of columnar layer is evenly
thickened with uniform, regularly arranged, and well devel-
oped columellae. Evidently, the two are not at the same
evolutional level. To consider the genus position of
Semenovia rubtzovii in relation to Heracleum L. the differ-
ences in their pollen exine characteristics may be an impor-
tant basis for systematic classification.
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