(c) Briefly describe the male and female strobili of Gnetum with suitable labelled diagrams. Why should you consider this plant a gymnosperm ?

Male Strobilus of *Gnetum*

The male strobilus of *Gnetum* is a compound structure, often appearing as a cluster at the tip of dwarf branches or in axillary positions. It resembles an inflorescence, sometimes described as a panicle type. Each male strobilus consists of a slender central axis with several stout, warted nodes. These nodes bear whorls of circular bracts fused to form cup-like structures known as collars or cupules. Multiple collars are typically arranged one above the other along the axis.

• Arrangement of Flowers: Above each collar, there are typically 3-6 whorls of male (staminate) flowers, with each whorl containing 20-40 sessile flowers. These flowers are arranged alternately in the rings.
• Male Flower Structure: Each male flower is small and consists of a perianth (formed by two coherent bracts) and two unilocular anthers attached to a short stalk. At maturity, the stalk elongates, causing the anthers to emerge from the perianth for pollen dispersal.
• Sterile Ovules: A distinctive feature of the male strobilus is the presence of a ring of abortive (sterile or imperfect) ovules located above the rings of male flowers in some species (e.g., *Gnetum gnemon*). These sterile ovules do not develop into seeds.

Diagram of Male Strobilus (Simplified):

[Imagine a central axis with multiple stacked collars. Above each collar, show rings of small, stalked male flowers with anthers. Above the topmost rings of male flowers, indicate a ring of smaller, undeveloped sterile ovules.]

(Note: In an actual exam, a clear, hand-drawn, labelled diagram would be provided here, showing the main axis, nodes, collars, male flowers with perianth and anthers, and sterile ovules.)

Female Strobilus of *Gnetum*

The female strobilus of *Gnetum* is also a compound structure, resembling the male strobilus in its young stage. It is borne on separate female plants, usually terminally or axially. It typically measures 5-7 cm long and consists of a short axis with nodes and internodes.

• Arrangement of Flowers: Similar to the male strobilus, each node bears two opposite leafy bracts that are fused to form a collar. Above each collar, a ring of 4-10 ovules (female flowers) is present. The number of ovules may be fewer on the upper collars.
• Ovule Structure: Each female flower consists of a short stalk and an ovule (megasporangium). A mature ovule is composed of a central nucellus, which is protected by three layers of envelopes or integuments.
• Innermost Integument: Elongates beyond the middle envelope to form a long micropylar tube or style, which aids in pollen capture. It is free from the nucellus except at the chalazal end.
• Middle and Outer Integuments/Perianth: These layers also contain stomata, sclereids, and laticiferous cells. The outer envelope often becomes fleshy and colored at maturity, contributing to the fruit-like appearance of the seed.
• Development: In a young strobilus, the collars are compact, and female flowers are tiny. As the cone matures, the internodes elongate, exposing the female flowers. Only a few ovules develop into mature seeds.

Diagram of Female Strobilus (Simplified):

[Imagine a central axis with multiple stacked collars. Above each collar, show a ring of larger, sessile ovules, each clearly showing the three integuments and a prominent micropylar tube.]

(Note: In an actual exam, a clear, hand-drawn, labelled diagram would be provided here, showing the main axis, nodes, collars, and ovules with their three integuments and the micropylar tube.)

Why *Gnetum* is Considered a Gymnosperm

*Gnetum* presents a unique set of morphological and anatomical features that make its classification historically controversial, often being considered a "phylogenetic puzzle" or an "intermediate" between gymnosperms and angiosperms. However, based on both morphological and increasingly robust molecular phylogenetic studies, it is firmly classified within the gymnosperms, specifically in the division Gnetophyta.

Key Gymnosperm Characteristics in *Gnetum*:

1. Naked Ovules/Seeds: The most defining characteristic of gymnosperms is the presence of ovules and seeds that are not enclosed within an ovary. In *Gnetum*, despite the presence of multiple envelopes around the ovule, these do not form a closed ovary wall that develops into a fruit. The seeds remain exposed or are only partially enclosed by fleshy bracts, not a true pericarp.
2. Reproductive Structures as Strobili/Cones: The male and female reproductive organs are organized into cones or strobili, a typical gymnosperm feature, rather than true flowers with a definitive perianth (sepals and petals) and carpels characteristic of angiosperms. While *Gnetum* strobili show some angiosperm-like organization, they lack true carpels.
3. Absence of True Fruits: Since there is no ovary, the characteristic development of a fruit (a mature ovary) enclosing the seeds does not occur. The fleshy outer layers of *Gnetum* seeds are derived from integuments or modified bracts, not from an ovary wall.
4. Tracheids with Bordered Pits: Like other gymnosperms, *Gnetum* possesses tracheids with bordered pits in its xylem, which are characteristic water-conducting elements in gymnosperms. While it also has vessels (an angiosperm-like trait), the presence of tracheids aligns it with gymnosperms.
5. Pollination by Wind (Anemophilous) and Insects: While *Gnetum* shows adaptations for insect pollination (e.g., sugary pollination drops, certain morphological features), wind pollination (anemophily) is also significant, a common mode in many gymnosperms.
6. Development of Prothallial Cell: The development of a prothallial cell in the male gametophyte is a feature shared with other gymnosperms.
7. Molecular Phylogeny: Modern molecular phylogenetic analyses consistently place Gnetales (including *Gnetum*) as a sister group to conifers, within the broader gymnosperm clade, rather than closer to angiosperms. This has resolved earlier debates based solely on morphological convergences.

Angiosperm-like Features (Convergent Evolution):

It is important to acknowledge the features that led to the historical confusion regarding *Gnetum*'s classification:

• Presence of Vessels in Xylem: This is a prominent feature otherwise found primarily in angiosperms, facilitating efficient water transport.
• Reticulate Venation in Leaves: The broad, elliptic leaves of *Gnetum* often exhibit a net-like or reticulate venation, similar to dicotyledonous angiosperms, contrasting with the typically simple or needle-like leaves of most gymnosperms.
• Double Fertilization: *Gnetum* exhibits a form of double fertilization, where two sperm cells from a single pollen tube participate. One fuses with the egg to form a zygote, and the other with another cell to produce a second zygote (rather than an endosperm as in angiosperms). This unique process is distinct from angiosperm double fertilization but shows a convergent evolutionary pathway.
• "Flower-like" Appearance of Strobili: The organization of reproductive units within the strobili can superficially resemble inflorescences of some angiosperms.

Despite these angiosperm-like convergences, the fundamental reproductive characteristics, especially the naked ovules and the overall genetic evidence, solidify *Gnetum*'s position within the gymnosperms.