General Features of Gymnosperms

Diversity of Seed Plants and their Systematics
Gymnosperms I
General Features of Gymnosperms and their Classification
Dr. NUPUR BHOWMIK
Department of Botany
University of Allahabad
Senate Hall
Allahabad – 211002
[email protected]
Date of submission: 27/06/2006
Keywords
Coniferophyta, nucellus, microsporophylls, ovule, archegonium, Pteridosperms, epiphyte, parasite, prothallial
cells, integument, dendrochronological, Cretaceous, Devonian.
GENERAL FEATURES OF GYMNOSPERMS AND THEIR CLASSIFICATION
Gymnosperms are seed plants that compose a major component of the temperate forests of the world. They are
widely appreciated for the great range of variation in habit and shapes. They have some of the tallest trees
known in the plant kingdom. Sequoia sempervirens, commonly called the Californian or "Coast Redwood"
because of its red coloured bark and red heart wood, reaches a height of 112 metres, and a diameter of 5
metres(See Pl. 1 & Pl. 2). Another species, Sequoiadendron giganteum from California, U.S.A. commonly
called "Big Tree" or the Wawona Tree, is a little shorter in length about (87m) but attains a diameter of more
than 10 metres (See Pl. 3).
The age of tallest tree is estimated from 400 to 800 years. The oldest redwood on record, which has a diameter
of 3.7 metres across is estimated to be 2,200 years. However, the distinction of being the oldest living tree on
earth has now gone to a species of Pinus, P. aristata now called as P. longavea. A tree of this species is growing
at 3275 m. above sea level in east Nevada-Utah State boundary(See Pl. 4). The age has been
dendrochronologically shown to be 4900 years old (Foster & Gifford, 1974). Other estimates of age of the oldest
tree of this species are mentioned as their being as old as 6000 years old (Sahni, 1990).
However, all gymnosperms are not tall and gigantic. There are some small herbaceous looking forms also, like
Zamia pygmaea and Stangeria paradoxa(See Pl. 5) or the two parasitic forms, Parasitaxus (= Podocarpus)
ustus(See Pl. 12) and Gnetum trinerve. While the former parasitises on Dacrydium taxoides, the latter is a
parasite in Cinchona forests of Chimboraza (Pearson, 1929). A species of Zamia, Z. pseudoparasitica is
exceptional among all gymnosperms in being epiphytic(See Pl. 6). A few gymnosperms may be lianas or
climbers.
They are mostly evergreen, but some such as Larix and Taxodium are deciduous(See Pl. 7). The plants are
mostly xerophytic but plants such as Taxodium are also known to grow in swamps or marshy places in Mexico
and Florida. (See Pl. 8)
The gymnosperms include ancient lines of seed-bearing plants whose evolutionary history dates back to the
Upper Devonian, roughly about 375 million years ago. One of the extinct gymnosperms consisted of an
assemblage of plants whose foliage was fern-like in general appearance yet it possessed a primitive type of seed.
This group of plants was named "seed ferns" or "pteridosperms". Undoubted gymnosperms had come into
existence during the Lower Carboniferous (about 355 million years back) and had reigned over the plant
kingdom by virtue of their dominance right upto the Cenomanian (about 96 million years from now) till the
advent of angiosperms at the end of the Cretaceous.
The surviving gymnosperms no longer dominate the plant kingdom but can still claim to own about 70 genera
and 800 species distributed in various parts of the world. They include the newly described genera Chigua and
Wollemia. While Chigua belonging to Zamiaceae of cycads was described by D.W. Stevenson in 1990(See Pl.
9), the genus Wollemia assigned to Araucariaceae of conifers was discovered a few years later by Hills et al.
(1996) (See Pl. 10). The largest group is the Coniferophyta, which includes pines, firs, cedars, spruces and
junipers which form extensive forests of northern and southern hemispheres. It contrast, living representatives of
the Ginkgophyta and Cycadophyta are veritable "living fossils", the former being represented by the sole living
member Ginkgo biloba (See Pl. 11) existing in wild state in certain mountains in southeastern China and the
latter are relicts from the past age being confined to limited areas in tropics and sub-tropics. The last group of
living gymnosperms is the Gnetophyta represented by Welwitschia, Ephedra and Gnetum.
Gymnosperms are highly valued for their timber. They are also sources of starch, resins, essential oils, drugs,
edible nuts etc. Many are cultivated as ornamental plants ("palms") and are found in gardens all over the world
while some conifers are sold as Christmas trees. Some gymnosperms like the Ginkgo are held in high esteem
and are found growing around Buddhist temples in China and Japan.
Gymnosperms (gymnos = naked, sperma = seed) include plants whose ovules are naked and freely exposed for
pollination. They are borne on microsporophylls, scales, or comparable structures. In angiosperms (angios =
closed, sperma = seed) ovules are enclosed in a carpel and usually completely closed at the time of pollination.
The sporophyte is usually arborescent comprising of large or small woody trees or shrubs. Few may be lianas or
climbers. Most gymnosperms are evergreen but some are deciduous such as Larix and Taxodium(See Pl.7). The
plants are mostly xerophytic. Gymnosperms show the following features:
1.
The plants have a long lasting tap root system. The vascular cylinder is di-to
polyarch, xylem exarch. Main elements of xylem are tracheids. Phloem is composed
of sieve cells and lacks companion cells. Some forms exhibit additional symbiotic
relationship between roots and algae in coralloid roots (Cycas) and between roots and
fungi in mycorrhizic roots (Pinus).
2.
The sporophyte shows unlimited growth of aerial trunk by means of apical and lateral
meristem which produce secondary vascular tissues.
3.
The aerial trunk is branched or unbranched and woody. Majority of gymnosperms
have branched stem (except in Cycas and Zamia). In Pinus branches are of two types
:- (a) long shoots or branches of unlimited growth (b) dwarf shoots or branches of
limited growth bearing clusters of variable number of needle shaped leaves and
collectively called as spur. Vascular bundle of stems are collateral, endarch or
mesarch, open and arranged in a ring.
4.
Secondary growth very pronounced. Secondary vascular tissues consisting mainly of
tracheids and sieve cells. Normally xylem lacks vessel elements and the phloem lacks
companion cells. But both vessels and companion cells present in members of
Gnetales. Mature metaxylem and secondary xylem elements have bordered pits of
various types. Wood or secondary xylem of two types namely, manoxylic and
pycnoxylic. In manoxylic type (as in Cycas) wood is less, porous and soft. There is a
large cortex and pith and parenchymatous rays are wide. In pycnoxylic type (as in
Pinus) wood is dense or compact with small xylem rays and reduced pith and cortex.
5.
Leaves are diverse in form and arrangement. They are both simple and compound
ranging in size from a minute scale to leaves a few meters long. Arrangements of
leaves usually spiral, they may also be whorled as in Cedrus or opposite decussate as
in Cupressaceae, Welwitshchia(See Pl. 12) and Gnetum. Scale leaves are
microphyllous whereas larger leaves are megaphyllous and their vascular supply
always leaves a leaf gap in the stem stele. Venation may be parallel (Agathis and
Welwitschia), reticulate (Gnetum) or dichotomous (Ginkgo) or as in most genera
there may be a single vein. Leaves may be dorsiventral or isobilateral, amphistomatic
or hypostomatic with sunken stomata. Mesophyll may be differentiated into spongy
and palisade parenchyma (Cycas, Gnetum) or undifferentiated (Pinus). Transfusion
tissue is a prominent feature. Leaf surface protected by a thick cuticle and sometimes
by an additional waxy layer. Resin canals occur in all conifers (except Taxus) and
mucilage ducts in cycads and Ginkgo and latex tubes in Gnetum. Vasculature of
petiole quite variable. In Cycas, vascular bundles are arranged in a horse-shoe shaped
manner or look like an inverted omega (U). They are diploxylic having both
centripetal and centrifugal xylem. In Ginkgo petiole receives two vascular bundles
and each half of lamina is supplied by one bundle which later dichotomizes. In
Gnetum, the petiole shows an arc-shaped arrangement.
6.
Vegetative methods of reproduction are rare in gymnosperms but vegetatively
propagating bulbils are known in Cycas.
7.
Plants are heterosporous. They may be monoecious (Pinus) or dioecious (Cycas).
Reproductive structures are borne in cones or strobili that are either staminate (male)
or ovulate (female) except in Cycas where ovules are borne on loose
megasporophylls. Sporangia are borne on fertile leaves or leaf-like structures called
microsporophylls (in male cone) and megasporophylla (in female cones) which are
arranged spirally around a central axis.
8.
Microsporangia are borne on abaxial or lower surface of microsporophylls. They may
be numerous and grouped in sori (Cycas) or reduced to two (Pinus). Microspores are
produced in tetrads.
9.
Megasporangium or ovule is borne on adaxial or upper surface of megasporophyll or
ovuliferous scale and are generally orthotropous. Young megasporangium consists of
a nucellus which is surrounded by a sheath or integument and inside the nucellus is
single functional megaspore. A narrow passage above the nucellus in the integument
is the micropyle.
10. Microspore and megaspore germination in situ, producing micro-and
megagametophytes which are not autotrophic. Microspores have partly developed
endosporic male gametophytes when they are transferred to micropyle of ovule. The
microspore or pollen grain at the time of shedding may have only one prothallial cell
(Cycas) or two prothallial cells (Pinus), the former being liberated at three-celled
stage and latter at four-celled stage.
11. The microspores or pollen grains are borne by wind and enter the ovule directly
through the micropylar canal. The micropyle in almost all gymnosperms secretes a
sugary exudate called the "pollination drop" which not only receives the pollen grains
but also transports them to nucellus of ovule.
12. The development of female gametophyte is monosporic (except in Welwitschia and
Gnetum where it is
tetrasporic). It is permanently retained inside the megaspore wall and dependent on
parent sporophyte for its nutrition. The archegonia in female gametophyte may be
two (in Ginkgo) to many (as in many conifers). Archegonia are quite large and
elongated and lack neck canal cells. Often the ventral canal cell too, is eliminated.
Gametophytic cells around the archegonia develop into a nutritive layer or jacket.
However, the nutritive layer and archegonia are absent in Welwitschia and Gnetum.
13. Fertilization is effected by means of a pollen tube (siphonogamy). The multiflagellate
spermatozoids or male cells within the pollen tube have no specialized means of
locomotion and occur within the ovule. The pollen tube bursts liberating two large
flagellated sperms into the cavity (archegonial chamber) directly above female
gametophyte. One sperm fertilizes the large egg cell giving rise to a zygote (2n).
14. At the beginning of embryogeny, zygote shows free nuclear division in all except
Welwitschia, Gnetum and Sequoia sempervirens. Later embryo becomes cellular after
wall formation and gradually differentiates into a suspensor, shoot apex, cotyledons,
hypocotyl and radicle. Polarity is endoscopic with the shoot end directed away from
the micropyle. Embryo remains contained within the seed developed from the ovule.
Mature embryo is differentiated into root, stem and leaves.
15. In most gymnosperms a common feature in embryogeny is polyembryony with
young seeds having more than one embryo. It may be simple polyembryony when
more than one archegonium is fertilized producing several zygotes or cleavage
polyembryony when single zygote gives rise to multiple embryos due to cleavage or
splitting of embryonal layer. The mature seed normally has only one embryo.
16. The young embryo draws its nutrition from the endosperm which develops before
fertilization and is haploid (n). Endosperm develops from female gametophyte that
has absorbed the food from nucellus.
17. During last phases of embryogeny, the nucellar tissue of ovule becomes disorganized
and frequently persists only as a paper-like cap of dry tissue at micropylar end of the
seed.
18. Gymnosperm ovules and seeds are unprotected and not surrounded by an ovary wall,
hence true fruits like that of angiosperms are not formed.
19. Histological maturation of various layers of integument continues and the stony layer
becomes an extremely hard, resistant shell which effectively encloses and
mechanically protects the female gametophyte and the embryo.
20. The detached seeds of all gymnosperms (except for cycads and Ginkgo) remain
dormant for sometime undergoing a resting period.
21. Gymnosperms being mostly temperate plants (except for cycads, Gnetum and
Ephedra) growing in tropics and subtropics show very little activity in the
development of reproductive structures during winter. The activity is renewed in the
spring. Under favourable conditions the embryo resumes growth and after rupturing
the seed coat develops into a new sporophyte plant.
22. Polyploidy is rare in gymnosperms, except in Juniperus (partly) Sequoia and
Ephedra (partly) where gametic number is multiple of the basic number of the
families. Sequoia is the solitary gymnosperm which is hexaploid. Ephedra is the only
genus where polyploidy is common.
Classification of Gymnosperms
Gymnosperms have been variously classified by different workers from time to time. The early history of
classification of gymnosperms is linked with the angiosperms. Robert Brown (1827), after recognizing the
gymnosperms as a distinct group of plants placed them alongwith angiosperms.
Benthem and Hooker (1862-1883) in their Genera Plantarum, placed them between the Dicotyledones and
Monocotyledones. They recognised only three orders of living gymnosperms: Gnetaceae, Coniferae and
Cycadaceae.
Some outstanding systems of classification of gymnosperms are being mentioned below:Van Tieghem (1898) recognized gymnosperms as one of the two major divisions of Spermatophyta.
Spermatophyta
Gymnosperms
(Astigmatae)
Angiosperms
(Stigmatae)
Eichler (1883), considered gymnosperms as one of the two divisions under. Phanerogamae. The second division
being Angiospermae. Eichler (1889) classified the seed plants as:
Phanerogamae
Gymnospermae
Cycadaceae
Cordaitaceae
Angiospermae
Coniferae
Pinioideae
Abietineae
Cupressineae
Gnetaceae
Taxoideae
Taxeae
Podocarpineae
By the beginning of the present century, Engler (1897), Coulter and Chamberlain (1910), Engler and Prantl
(1926), Rendle (1930) and others recognized gymnosperms as a primary division of Spermatophyta,
Phanerogamia or Embryophyta-Siphonogama. They divided the group into classes or orders of coordinate rank,
viz. (1) Pteridospermae (Cycadofilicales) (2) Cycadales (3) Bennettitales (4) Cordaitales (5) Ginkgoales (6)
Coniferales and (7) Gnetales.
Sahni (1920a) recognised two main phyletic lines in the orders of gymnosperms based on the difference
between the morphological nature of the ovule bearing organs of cycads and conifers. He classified
gymnosperms in the following way:
Gymnosperms
Phyllospermae
Pteridosperms
Cycadales
Cordaitales
Stachyospermae
Bennettitales
Ginkgoales
Coniferales
Taxales (including Taxus, Torreya
and Cephalotaxus)
Chamberlain (1935) classified gymnosperms into:
Gymnosperms
Cycadophytes
Gymnosperms with fern-like pinnatifid
leaves, weakly branched large globose or
columnar trunks, having large conspicuously
developed pith and cortical zones in stem.
Secondary xylem cylinder small, composed
mainly of tracheids and abundant
parenchyma (manoxylic wood). Group well
represented in fossil record. The only
surviving representatives are the modern
cycads.
Orders 1. Cycadofilicales
2. Bennettitales
3. Cycadales
Coniferophytes
Gymnosperms with profusely branched
trunks, leaves simple (needle-like, scale-like
or laminate), stems with small pith and
cortex. Secondary xylem cylinder massive
and less parenchymatous (pycnoxylic wood).
The group includes extinct as well as extant
orders like:Orders: 1. Cordaitales
2. Voltziales
3. Coniferales
4. Ginkgoales
5. Gnetales
Extinct
Extinct and
living
Arnold (1948) recognized three classes under gymnosperms.
Gymnosperms
Classes
Orders
Cycadophyta
1. Pteridospermales
2. Cycadeoidales
3. Cycadales
Coniferophyta
1. Cordaitales
2. Ginkgoales
3. Taxales
4. Coniferales
Chlamydospermophyta
1. Ephedrales
2. Gnetales
Pant (1957) suggested a classification which is a modification of Arnold's classification. The three classes of
Arnold have been raised to the rank of divisions:Gymnosperms
Division: Cycadophyta
Plants with relatively small,
usually unbranched or poorly
branched aerial or subterranean
trunks; leaves usually large and
pinnate; stems have large pith, a
thick cortex, scanty wood usually
with wide medullary rays
(manoxylic)
Class 1 Pteridospermopsida
Orders 1. Lyginopteridales
2. Medullosales
3. Glossopteridales
4. Peltaspermales
5. Corystospermales
6. Caytoniales
Class 2 Cycadopsida
Order 1. Cycadales
Class 3 Pentoxylopsida
Order 1. Pentoxylales
Class 4 Bennettitopsida
Pant (2002) in a
(Cycadeoideopsida)
Order 1. Bennettitales
(Cycadeoideales)
Chlamydospermophyta
Peculiar angiosperm-like
forms
Class 1 Gnetopsida
Orders 1. Gnetales
2. Welwitschiales
Coniferophyta
(Pinophyta)
Usually large sized trees,
with profusely branched
stems and simple leaves.
Stems have small pith,
narrow cortex, abundant
compact wood usually with
narrow medullary rays
(
li )
Class 1 Coniferopsida
(Pinopsida)
Orders 1. Cordaitales
2. Coniferales
(Pinales)
3. Ginkgoales
Class 2 Epedropsida
Order 1. Ephedrales
Class 3 Czekanowskiopsida
Order 1. Czekanowskiales
Class 4 Taxopsida
Order 1. Taxales
Later publication suggested that separation of Taxopsida-Taxales was not valid in view of the work of Harris
(1976) and others and accordingly merged this class and order with his order Coniferales (Pinales) and placed
plants of this group under family Taxaceae under order Coniferales.
Andrew's (1961) classification included six divisions under the gymnosperms:
Gymnosperms
Divisions Pteridospermophyta
Order 1. Pteridospermales
Ginkgophyta
Order 1. Ginkgoales
Coniferophyta
Orders 1. Coniferales
2. Cordaitales
Cycadophyta
Orders 1. Cycadales
2. Bennettitales
Order
Gymnosperms of uncertain
origin
Orders 1. Pentoxylales
2. Vojnovskiales
Gnetophyta
1. Gnetales
Sporne (1974) recognized three classes under the gymnosperms:
Gymnosperms
Class 1 Cycadopsida
Orders 1. Pteridospermales
2. Bennettitales
3. Pentoxylales
4. Cycadales
Class 2 Coniferopsida
Orders 1. Cordaitales
2. Coniferales
3. Taxales
4. Ginkgoales
Class 3 Gnetopsida
Order 1. Gnetales
Steward (1983) placed under the division Trachaeophyta of plant kingdom three distinct classes :Plant Kingdom
Trachaeophyta
Class 1 Progymnospermopsida
Orders 1. Aneurophytales
2. Archaeopteridales
3. Protopityales
Atrachaeophyta
Class 2 Gymnospermopsida
Orders 1. Pteridospermales
2. Cycadales
3. Cycadeoidales
4. Caytoniales
5. Glossopteridales
6. Pentoxylales
7. Czekanowskiales
8. Ginkgoales
9. Cordaitales
10. Voltziales
11. Coniferales
12. Taxales
Class 3 Gnetopsida
Orders 1. Gnetales
2. Ephedrales
3. Welwitschiales
Meyen (1984, 1986) has suggested a classification wherein under the division Pinophyta (= Gymnospermae) he
included three classes, viz. Ginkgopsida, Cycadopsida and Pinopsida. He placed the angiosperms under the
division Magnoliophyta. According to Pant (2002) one of the novelties of Meyen's classification was the
recognition of Ginkgopsida for the first time as a Class. The other two Classes had already been recognized
earlier. Meyen (1984, 1986) had assigned nine Orders under this Class which included diverse gymnosperms,
and most of the Orders included families which are based on incompletely known fossil forms. In fact, Pant
(2002) believes that the Class was created to dump all such diverse imperfectly known forms which could not be
fitted in the two other Classes. The Class included two living genera, Ginkgo with a single living species G.
biloba besides several imperfectly known fossils and Ephedra with about fifty species. Both the genera showed
resemblances with Class Pinopsida.
Class Cycadopsida had six Orders which included Gnetales and Welwitschiales and Class Pinopsida had two
Orders, viz. Cordaitanthales and Pinales (Coniferales). While appreciating Meyen's system as a good survey
Bhatnagar and Moitra (1996), felt the placement of Ephedrales, Gnetales and Welwitschiales appeared highly
unsatisfactory.
Gifford and Foster (1989) considering the general tendency in recent years to establish several major taxa of
extinct and living gymnosperms have raised the important groups to the rank of Division. Their classification of
gymnosperms lists only the major Divisions and selected Orders. The occurrence of the Divisions and Orders in
the geologic time is also indicated viz.
Gymnosperms
Division
Geologic Time
Middle Devonian to Lower
Carboniferous
Div. 1 Progymnospermophyta
Orders Aneurophytales
Archaeopteridales
Div. 2 Pteridospermophyta
Orders Glossopteridales
Carboniferous to Permain
Caytoniales
Div. 3
Order
Cycadophyta
Cycadales
Div. 4
Order
Cycadeoidophyta
Cycadeoidales
Div. 5
Order
Ginkgophyta
Ginkgoales
Div. 6
Coniferophyta
Permian to Triassic (Glossopteridales)
Triassic to Cretaceous (Caytoniales)
Permian to Recent
Triassic to Cretaceous
Triassic to Recent
Upper Carboniferous to Permian
Orders Cordaitales
Div. 7
Voltziales
Coniferales
Gnetophyta
Upper Carboniferous to Permian
(Cordaitales)
Upper Carboniferous to Jurrasic
(Voltziales)
Triassic to Recent (Coniferales)
Permian (?) to Recent
Orders Ephedrales
Gnetales
Welwitschiales
Kramer & Green (see Kubitzki, 1990) have classified the Division Gymnosperms into two Subdivision as
follows:Division
Subdivision
Classes Cycadatae
Order Cycadales
Families 1. Stangeriaceae
2. Boweniaceae
3. Cycadaceae
4. Zamiaceae
Gymnosperms
Cycadophytina
Gnetatae
Gnetales
1. Ephedraceae
2. Gnetaceae
3. Welwitschiaceae
Coniferophytina
Ginkgoatae
Ginkgoales
1. Ginkgoaceae
Pinatae
Pinales (Coniferales)
1. Taxaceae
2. Cephalotaxaceae
3. Phyllocladaceae
4. Podocarpaceae
5. Araucariaceae
6. Sciadopityaceae
7. Taxodiaceae
8. Cupressaceae
9. Pinaceae
According to Bhatnagar & Moitra (1996) the clubbing of Gnetales with Cycadales is unjustified.
Bhatnagar and Moitra (1996) adopted a classification in their book entitled, "Gymnosperms", which is a
synthesis of views prevalent in recent years. The classification is as following:
Gymnosperms
Division
Classes Progymnospermopsida
Class 1 Progymnospermopsida
Orders 1. Aneurophytales
2. Archaeopteridales
3. Protopityales
Cycadopsida
Family: Aneurophytaceae
Family: Archaeopteridaceae
Family: Protopityaceae
Class 2 Cycadopsida
Orders 1. Pteridospermales
Families 1. Calamopityaceae
2. Lyginopteridaceae
3. Medullosaceae
4. Callistophytaceae
Order 2 Glossopteridales
Family: Glossopteridaceae
Coniferopsida
Class 3 Coniferopsida
Orders 1 Coniferales
Families 1. Pinaceae
2. Taxodiaceae
3. Cupressaceae
4. Podocarpaceae
5. Araucariaceae
6. Cephalotaxaceae
7. Taxaceae
Order 2 Ginkgoales
Family: Ginkgoaceae
Order 3 Czekanowskiales
Family: Czekanowskiaceae
Order 4 Cordaitales
Family: Cordaitaceae
Order 5 Voltziales
Order 3 Caytoniales
Families 1. Caytoxiaceae
2. Corystospermaceae
3. Peltaspermaceae
FOSSILIZATION AND SOME FOSSIL GYMNOSPERMS
Class 4 Gnetopsida
Order 4 Cycadales
Family: Cycadaceae
Orders 1 Ephedrales
Order 5 Cycadeoidales (Bennettitales)
Suggested readings Order 2 Gnetales
Families 1. Williamsoniaceae
2. Wielandiellaceae
1.
Fossil by Mark Lambert, A Kingfisher Book, Ward. Lock Limited, London.
Order 3 Welwitschiales
3. Cycadeoidaceae
2.
Nature Library- Fossils by Richard L. Moody.
Order 6 Pentoxylales
Family: Pentoxylaceae
3.
Gnetopsida
The Biology and Evolution of Fossil Plants by T.N.
Family: Voltziaceae
Family: Ephedraceae
Family: Gnetaceae
Family: Welwitschiaceae
13
Suggested readings:
1.
GREEN PLANTS Their origin and Diversity - by Peter R. Bell & Alan R. Hemsley (2000) Cambridge
University Press.
2.
AN INTRODUCTION TO GYMNOSPERMS, CYCAS AND CYCADALES - by Divya Darshan Pant
(2002) Birbal Sahni Institute of Palaeobotany, Lucknow, India.
3.
GYMNOSPERMS - by S.P. Bhatnagar & Alok Moitra (1996) New Age International Limited.
4.
MORPHOLOGY AND EVOLUTION OF VASCULAR PLANTS - by E.M. Gifford, & A.S. Foster (1989)
W.H. Freeman & Co., New York.
5.
MORPHOLOGY OF VASCULAR PLANTS - by D.W. Bierhorst (1971), The Macmillan Co., New York.
6.
MORPHOLOGY OF GYMNOSPERMS - by J.M. Coulter & C.J. Chamberlain, (1917), University Chicago
Press, Chicago.
7.
GYMNOSPERMS: STRUCTURE AND EVOLUTION - by C.J. Chamberlain (1935), Chicago Univ. Press,
Chicago.
8.
STUDIES IN GYMNOSPERMOUS PLANTS. CYCAS - by D.D. Pant & B. Mehera (1962), Central Book
Depot, Allahabad.
9.
LIVING INDIAN GYMNOSPERMS. Pt. I (Cycadales, Ginkgoales and Coniferales) - by M.B. Raizada and
K.C. Sahni (1960) Ind. For. Rec. (N.S.) Bot. 5: 73-150.
10. THE PRIVATE LIFE OF PLANTS - by David Attenborough (1995), BBC Enterprises, Ltd. Woodlands,
London.
11. CONIFERS - THE ILLUSTRATED ENCYCLOPEDIA. Vol. I & II - by D.H. van Gelderen & J.R.P. van
Hoey Smith (1996), Timber Press, Inc. Orgon, U.S.A.
14
Plate 1
Sequoia sampervirens, Coast Redwood, Native to Northern California, U.S.A. (Reproduced
from “The Private Life of Plants” by David Attenborough, 1995)
15
Plate 2
A
B
Sequoia sampervirens, Coast Redwood. A: Showing remarkably small cones of this giant tree.
B: Giant trees (All photographs reproduced from “Conifers- The Illustrated Encyclopedia” by
D.M. Van Gelderen and J.R.P. Van Hoey Smith, 1996)
16
Plate 3
A
B
Sequoiadendron giganteum. A: Trunks of two gigantic trees growing in Mariposa Grove,
California, U.S.A. B: A tree in a U.S. National Park with the nick name “Grizzly Giant.”
(All photographs reproduced from “Conifers- The illustrated Encyclopedia” by D.M. Van
Gelderen and J.R.P. Van Hoey Smith, 1996)
17
Plate 4
Pinus longavea, the longest living organism on earth growing at 10,000 ft. in White mountains of Eastern C
age of some has been estimated at about 4,600 years. (Photograph reproduced from “The Private Life
Attenborough, 1995)
Plate 5
18
A
B
C
D
Zamia pygmaea. A: Showing leaf details. B: Showing female cones
Stangeria (paradoxa) eriopus. C: Forest form showing leaf details. D: Forest form showing
habitat. (All Photographs reproduced from “The Cycads” by Loran M. Whitelock, 2002)
Plate 6
19
A
B
C
Zamia pseudoparasitica. A, B: Male and female cones. C: Showing epiphytic habit in
habitat near El Cope, Panama. (All Photographs reproduced from “The Cycads” by Loran
M. Whitelock, 2002)
Plate 7
20
A
B
C
D
Larix decidua. A, B: Deciduous trees, also called as a “witches” broom C: Same plant as
above in winter. D: A tall and slender tree with pendulous branches. The tree is very
valuable for its timber. (All photographs reproduced from “Conifers- The illustrated
Encyclopedia” by D.M. Van Gelderen and J.R.P. Van Hoey Smith, 1996)
Plate 8
21
C
B
A
Taxodium distichum. A: The Bald Cypress or Swamp Cypress in its native habitat along
the Alatamaha river, Georgia, U.S.A. B: Showing male inflorescences and female cones.
C: The respiratory “knees” of this species, as growing in Breukelen, The Netherlands.
(All photographs reproduced from “Conifers- The illustrated Encyclopedia” by D.M. Van
Gelderen and J.R.P. Van Hoey Smith, 1996)
Plate 9
22
A
B
C
Chigua restrepoi. A: Showing an entire male plant. B: Showing leaf details. C: Showing
male cones. (Figure and photographs reproduced from “The Cycads” by Loran M.
Whitelock. 2002)
Plate 9
23
A
B
C
Chigua restrepoi. A: Showing an entire male plant. B: Showing leaf details. C: Showing
male cones. (Figure and photographs reproduced from “The Cycads” by Loran M.
Whitelock. 2002)
24
Plate10
B
C
A
Wollemia nobilis. A: Showing habit, shoots with male and female cones and a seed on
ovuliferous scale. B: Showing the warty bark. C: A young specimen with typical needles.
(Photographs reproduced from “Conifers- The Illustrated Encyclopedia” by D.M. Van
Gelderen and J.R.P. Van Hoey Smith, 1996 and figures courtesy D.K. Chauhan)
Plate 11
25
B
A
C
D
Ginkgo biloba. A: A specimen of the Maidenhair Tree, growing in Sendai, Japan, said to be 1,000
years old. B: Another tree, in winter. C: Showing male inflorescence. D: Showing the fruits and
autumn colours of leaves. (All Photographs reproduced from “Conifers- The illustrated
Encyclopedia” by D.M. Van Gelderen and J.R.P. Van Hoey Smith, 1996)
Plate 12
26
A
B
C
D
Welwitschia mirabilis. A: A large plant growing at the shore of the Atlantic Ocean, Namibia. B:
A female specimen of this species showing the inflorescences.
Parasitaxus ustus. C: The only known parasite conifer, seen in its habitat in New Caledonia,
where it grows on roots of the only known host, Dacrydium taxoides. D: A small shrub of the
same species producing coppery red leaves that are scale-like and triangular in shape. (All
photographs reproduced from “Conifers- The illustrated Encyclopedia” by D.M. Van Gelderen
and J.R.P. Van Hoey Smith, 1996)