Gnetum, a dioecious genus, presents unique reproductive strobili.

Male Strobilus of Gnetum
The male strobilus is compound, appearing as a spike. It features a central axis with nodes bearing cup-shaped collars formed by fused bracts. Above these collars, several whorls of male flowers are present. Each reduced male flower typically has a perianth and two stamens (microsporangiophores) with two anthers. Interestingly, a whorl of abortive (sterile) ovules is often found at the top of each collar.

Female Strobilus of Gnetum
The female strobilus is also compound and cone-like. It similarly has a central axis with nodes bearing cup-shaped collars. Within the axil of each collar, one to several fertile ovules are present. Each orthotropous ovule is encased by multiple envelopes: an inner integument, a middle envelope, and an outer fleshy envelope. Usually, only the uppermost ovules are fertile.

Why Gnetum is considered a Gymnosperm:
Despite exhibiting angiosperm-like traits such as compound strobili, simple leaves with reticulate venation, and the presence of vessels in its xylem, Gnetum is classified as a gymnosperm due to fundamental reproductive characteristics:

1. Naked Ovules: Crucially, its ovules are not enclosed within an ovary, a defining feature of gymnosperms. They are directly exposed for pollination. The envelopes are not homologous to angiosperm carpels.
2. Absence of True Fruits: Lacking an ovary, Gnetum does not form true fruits (a mature ovary) after fertilization.
3. Direct Pollination: Pollen lands directly on the exposed ovule via a pollination drop, not on a stigma.
4. Unisexual Strobili: The presence of distinct male and female cones, even if compound, aligns with gymnosperm reproduction.

These core reproductive traits firmly place Gnetum within the gymnosperm lineage.