Pant, D. D.

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OPINION
CURRENT SCIENCE, VOL. 79, NO. 3, 10 AUGUST 2000278
Inclusion of Taxaceae in a separate order, Taxales
D. D. Pant
Taxus and its related genera, viz. Torreya,
Austrotaxus, Pseudotaxus and Amentotaxus
were unquestionably included in the
Pinales (= Coniferales) although they
were usually included in a family of their
own, the Taxaceae, inclusive of Cephalo-
taxus by Coulter & Chamberlain1 or ex-
clusive of Cephalotaxus by Pilger2,
who placed Cephalotaxus in a separate
family, the Cephalotaxaceae. However,
in 1920, Sahni3 suggested that Taxus,
Torreya and other closely-related genera
and Cephalotaxus were so different from
other conifers and they should be inclu-
ded in a separate order Taxales. Sahni’s
suggestion about a wider separation of
Taxus in a separate order Taxales was
supported by Florin4, but he pointed out
that Cephalotaxus should continue un-
disturbed in the Pinales since it did have
a female cone, although it was much
reduced but Taxus alone was radically
different from Coniferales because it had
no female cone and its female dwarf
shoot ended in a terminal ovule (Figures
1 a, b and 2 a). The unique peltate radi-
ally organized microsprophylls of Taxus
(Figure 1 c, d ) seemingly supported the
above wider separation of the Taxales.
Another point which may have prompted
Florin4 to plead for a wider separation of
Taxaceae in the Taxales was the lack of
any fossils which showed characters
linking Taxaceae with any other conifers.
The earliest taxads like Palaeotaxus
redeviva Florin (Figure 2 b) and Marskea
thomasii Harris (Figure 2 c) take us back
into the Lower and Middle Jurassic, res-
pectively, but there they leave us in the
lurch about their links with any other
groups of conifers or other gymnosperms.
The only genus of Taxus-like fossil shoots
reported from the Palaeozoic Lower
Gondwana rocks is Searsolia oppo-
sitifolia Pant & Bhatnagar5 but except for
some vague carbonless rounded impres-
sions of frutification-like bodies on a
shoot, its reproductive parts are unknown
(Figure 2 d ). Thus except for giving
overwhelming weight to the evidence of
a terminal ovule and the absence of a
female cone in the Taxales, neither Sahni3
nor Florin4 seems to have taken into con-
sideration the various characters which
are common to the Pinales and their new
order Taxales. The present article is
therefore intended to have a fresh look at
the similarities and differences between
Taxaceae and other conifers to enable us
to decide whether we can continue to
keep the Taxaceae as a family within the
Pinales or to include them in that family
under a separate order, the Taxales.
  As Chamberlain6 had pointed out, ‘the
grouping into families and sequence of
families will depend upon each investi-
gator. If he is an anatomist, anatomy will
determine the treatment. If strobili are
considered more important, they will
determine the grouping and sequence. If
gametophytes are emphasized, there will
be still another arrangement’. Therefore,
in order to eliminate individual bias it
seems to be necessary to take diverse
characters of the Pinales, exclusive of
Taxaceae and of the Taxaceae into con-
sideration in order to decide whether the
Taxaceae need to be separated widely
under Taxales as suggested by Sahni3
and Florin4 or kept within the Pinales
(= Coniferales).
  In their habitats and habit the Taxaceae
are quite like many other Pinales. They
are woody pycnoxylic shrubs and trees
inhabiting locations like those of the
Pinales. Their leafy shoots and simple
leaves are similar to those of many coni-
fers. Their secondary xylem no doubt is
peculiar in showing tertiary spirals, some-
times called taxinean spirals, but these
occur in Cephalotaxus as well.
  Among characters of Taxus which have
been mentioned as altogether different
from those of all other Pinales, are its radi-
ally organized peltate microsporophylls
with sporangia attached on the adaxial,
inner side. However, other genera of the
Taxaceae have dorsiventral microsporo-
phylls with microsporangia attached on
the abaxial, underside like those of the
Pinales. Thus, if we take the character of
peltate microsporophylls into considera-
tion we can widely separate Taxus alone
into Taxales but the microsporophylls of
the other genera conform with those of
the Pinales.
  The development and structure of the
male and the female gametophytes in the
Taxaceae are quite comparable with those
in the rest of the Pinales. Finally an intri-
cate character of the Pinales like the
tiered arrangement of the proembryo,
which is characteristic of all conifer pro-
embryos is also found in the Taxaceae as
shown by Sterling7 (see Figure 3).
  The basic chromosome number too is
n = 12 in Taxus, but Torreya and Amen-
totaxus have n = 11 (see Khoshoo8 and
Mehra9) and these numbers too are quite in
conformity with those prevalent in most of
the Pinales.
Figure 1. Taxus baccata. a, Twig-bearing
mature seeds with a surrounding aril; b,
Longitudinally split mature seeds inside aril;
c, Twig showing mature male ‘flowers’;
d, A peltate microsporophyll. a, b, after
Kerner, 1895; c, d, after Kerner, 1913.
c dba Figure 2. a, Taxus canadensis longisec-
tion of female dwarf shoot and terminal
ovule. b, c, Female flowers of Palaeo-
taxus rediviva and Marskea thomasii
respectively; d, Searsolia oppositifolia,
showing a leafy shoot with secondary
foliate branches and three shortly stalked
globose over the main axis.
c
d
b
a
OPINION
CURRENT SCIENCE, VOL. 79, NO. 3, 10 AUGUST 2000 279
  Therefore, taking into consideration all
the above characteristics of the Taxaceae
we find that the only character which is
regarded as categorically supporting their
wider separation into Taxales are their
terminal ovules in their female dwarf
shoots. However, as pointed out by
Harris10,11, a lateral ovule in a fertile
dwarf shoot like that of Lebachia, can be
assumed to have become terminal by the
abortion of the dwarf shoot apex and
Harris has cited examples from the angio-
sperms where this actually occurs (Figure
4). Moreover, as mentioned by Miller12
in his table 10.2 dealing with character
states of the OTU used in the CLINCH
and PAUP analysis, terminal ovules occur
also in Phyllocladus, Microcachrys
Saxegothaea of the Podocarpaceae,
Araucaria of the Araucariaceae and Cal-
litris of the Cupressaceae.
  We may thus conclude after taking all
the above facts into consideration, that
the assignment of Taxus and its allied
genera to the family Taxaceae appears to
be fully justified but their wider separa-
tion in a separate order of their own, the
Taxales, is supported solely by the termi-
nal position of their ovules in their
female dwarf shoots and according to
Miller12 (as mentioned above) this termi-
nal position too is shared by a few mem-
bers of the Pinales. Moreover, the ovules
could have become terminal by the abor-
tion of their dwarf shoot apices as sug-
gested by Harris10,11. Further, the cones
of Pinales could indeed be derived from
the scattered condition of female dwarf
shoots like those in Taxus to a condition
where they become crowded and inserted
at each node in pinalean cones as envis-
aged by Pant & Nautiyal13 and Pant14
(see Figure 5). The cumulative evidence
of all the diverse characters of Taxus and
its allied genera, as discussed above, is
therefore, adjudged as being strongly
against their wider separation in the order
Taxales.
 1. Coulter, J. M. and Chamberlain, C. J.,
Morphology of Gymnosperms, University
of Chicago Press, Illinois, 1917.
 2. Pilger, R., in Die Naturlichen Pflanzen-
familien (eds Engler, A. and Prantl, K.),
Ed. 2 Bd. 13 Engelmaun, Leipzig, 1926.
 3. Sahni, B., Ann. Bot., 1920, 34, 117–133.
 4. Florin, R., Bot. Gaz., 1948, 110, 31–39.
 5. Pant, D. D. and Bhatnagar, S., Palaeonto-
graphica B, 1975, 152, 191–199.
 6. Chamberlain, C. J., Gymnosperms, Struc-
ture and Evolution, University of Chi-
cago Press, Illinois, 1935.
 7. Sterling, C., Bull. Torrey Bot. Club,
1948, 75, 147–165.
 8. Khoshoo, T. N., in Proc. Summer School
in Botany, Darjeeling (eds Maheshwari
P., Johri, B. M. and Vasil, I. K.), Min.
Sci. Res. and Cul. Affairs, New Delhi,
1962, pp. 119–135.
 9. Mehra, P. N., Conifers, Gnetophytes and
Phylogeny of Gymnosperms, 1988.
 10. Harris, T. M., Rev. Palaeobot. Palynol.,
1976, 21, 119–134.
 11. Harris, T. M., The Yorkshire Jurassic
Flora 5, Coniferales British Museum
(Nat. Hist.) London, 1979.
 12. Miller Jr., C. N., in Origin and Evolution
of Gymnosperms (ed. Beck, C. B.),
Columbia University Press, NY, 1988.
 13. Pant, D. D. and Nautiyal, D. D., Philos.
Trans. R. Soc. London B., 1967, 774, 27–
48.
 14. Pant, D. D., J. Indian Bot. Soc., 1977,
56, 23–37.
D. D. Pant lives at 106, Tagore Town,
Allahabad 211 002, India.
Figure 3. Taxus. a, Secondary pro-
embryo with upper (U), suspensor (S) and
embryonal (E) tiers; b, Same at a later
stage showing a few surrounding gameto-
phytic cells; c, Young proembryo (e) with
differentiated embryonal tubes and with one
of its cells separated (all after Sterling7).
cb
a
Figure 4. Hypothetical longisections of
different onyogenetic stages of apices
of an early Taxus ancestor. a, Youngest
stage with raised apical meristem and
shoulders which will form scales; b, as a
but older with apex flattening, c, as b but
older, two ovules marked ‘o’ are beginning
to form; c′, as c but with one median
ovule. d ′, as c but older, the dormant
shoot apex bulges between the two integu-
mented ovules; d′ as c′ but older with a
terminal ovule (all after Harris10).
c′
d′
ba
c
d
Figure 5. Buriadia heterophylla. a, Bran-
ched shoot showing attached ovules;
b, Portion of shoot showing an attached
anatropous ovule among leaves; c, A
reconstructed hypothetical shoot showing
laterally attached solitary seeds among
leaves on branches of all orders; d, Axis
of a plant (hypothetical) with seeds as in
Buriadia but borne only on some unre-
duced lateral branches; e, Axis of a plant
(hypothetical) with reduced lateral bran-
ches; f, Hypothetical axis like e but with
fertile short shoots clustered around a
specialized lateral branch; g, Reconstruc-
ted shoot of Lebachia piniformis with ter-
minal cones. Figure on the right side
shows a cone with its basal part longitudi-
nally split (after Pant and Nautiyal13).
e f
c
d
a
g
b


Inclusion of Taxaceae in a separate order, Taxales

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Inclusion of Taxaceae in a separate order, Taxales

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