Classification of Gymnosperms

Due to the occurrence of gymnosperms in large groups (that may be both fossil or living forms), the classification of gymnosperms has become complicated to understand. A different worker classified gymnosperms into various classes. 

Some of the important classifications are as follows:

In 1917 Counter and Chamerlain classified the gymnosperm into seven orders which are:

1. Cycadofilicals
2. Benenrttitales
3. Cacadales
4. Cordaitales
5. Ginkoalea
6. Coniferales
7. Gnetales

In 1934, Chamberlain categorized gymnosperms into two classes which are further divided into different orders.

1. Class: Cycadophyte (it is divided into three orders)

• Order: Cycadofilicales
• Order: Cycadeiodales
• Order: Cycadales

2. Class: Coniferophyta (it is divided into four orders)

• Order: Cordaitales
• Order: Ginkgoales
• Order: Coniferales
• Order: Gnetales

 In (1948), Gymnosperms were divided into three phyla by Arnold

1. Phylum: Cycadophyta (it includes three orders)

• Order 1: Pteridosparmales
• Order 2: Cycadeoidales 
• Order 3: Cycadales

2. Phylum: Coniferophyta (it includes four orders) 

• Order1: Cordaitales
• Order 2: Coniferales
• Order 3: Taxales 
• Order 4: Ginkgoales

3. Phylum: Chlamydospermophyta (it includes two orders)

• Order 1: Ephedrales
• Order 2: Gnetales

After that in 1961, Andrew classified gymnosperm into 6 divisions:

1. Pteridospermatophyta
2. Cycadohyta
3. Coniferophyte
4. Ginkgohyta
5. Gnetophyta
6. Gymnosperms of uncertain affinities

In 1965, K.R. Sporne in his book named “The Morphology of Gymnosperms” classified gymnosperm into 3 divisions based on Pilger and Melchior (1954) classification, these divisions were further classified into orders.

A. Cycadopsida

Order 1: Pteriodospermales (it includes 7 families)

1. Lyginopteridaceae
2. Medulosaceae
3. calamopteridaceae
4. Glossopteridaceae
5. Peltospermaceae
6. Corystospermaceae
7. Caytoniaceae

Order 2: Bennettitales (it includes 3 families)

1. Williamsoniaceae
2. Wielandiellaceae
3. Cycadeoideaceae

Order 3: Pnetoxylaes (only one family)

1. Pentoxylaceae

Order 4: Cycadales(it includes 2 families)

1. Cycadaceae
2. Nilssoniaceae

B. Coniferopsida

Order 1: Cordaitales (it includes 3 families)

1. Ertophytaceae
2. Cordaitaceae
3. Poroxylaceae

Order 2: Coniferales (it includes 9 families)

1. Lebachiaceae
2. Vitziaceae
3. Palissyaceae
4. Pinaceae
5. Taxodiaceae
6. Cupressaceae
7. Podocarpaceae
8. Cephalotaxaceae
9. Araucariaceae

Order3: Taxales (only one family: Taxaceae)

Order 4: Ginkgoales (contains 2 families)

1. Trichoptyaceae
2. Ginkgoaceae

C. Gnetopsida

Order 1: Gnetales (includes 3 families)

1. Gnetaceae
2. Welwitschiaceae
3. Ephedraceae 

In the modern classification, gymnosperms are divided into four main orders.

A. Cyadales

• They are dioecious (meaning: separate male or female).
• Cyadales group of gymnosperms are found in tropical areas that originally originated in the Triassic period.
• Cyadales are represented by both living members and fossils.
• They are woody, wood is monoxylic.
• Leaves are pinnately compound. Young leaves with Circinate Ptyxix.
• Megasporophyll does not form female cones, Cyadales cones are large with many fertile leaves. E.g. sporophylls arranged into cones.
• Male gamete is motile.
• Cycadales are commonly called pandas of the plant kingdom.
• They are used as ornamental plants because their shape is beautiful. 
• Examples: Cycas, Zamia.

B. Ginkgoales

• Ginkgoales are represented by living members.
• Wood is pycnoxylic.
• Sperm are motile and contains spiral bands of flagella and multicillated.
• Dichotomous venation is generally present in the leaves.
• Ginkgoales contain only one extant species which is Ginkgo biloba.

C. Coniferales

• They have a sporophytic plant body and the sporophytes are richly branched trees or shrubs.
• Vessels are absent.
• Wood is monoxylic.
• Schizogenous canals present that form resin.
• Male gametes are non-motile and multicliated and male and female cones are present in Coniferales.
• Example: Sequoia, pinus, Thuya, Taxus, Aravcaria, etc.  

D. Gnetales

• They form connecting link between angiosperm and gymnosperms.
• Wood is pycnoxylic.
• Shrubs and small trees belong to Gnetales.
• The reproductive structure of Gnetales orders plants is almost similar to flowering plants.
• Embryo with 2 cotyledons.
• The ovule is nacked but bitegmic.
• Examples: Gnetum, Ephedra, Welwischia.