Q.59 Vessels are present in:
1. Cycas
2. Zamia
3. Ginkgo
4. Gnetum
Vessels are present in Gnetum among these gymnosperms, a unique feature setting the Gnetales apart from vessel-less Cycas, Zamia, and Ginkgo. This advanced xylem trait links Gnetum closer to angiosperms.
Gymnosperm Xylem Basics
Gymnosperms typically have xylem with tracheids only—no vessels—unlike angiosperms where vessels enhance water conduction efficiency.
Vessels (perforated end walls) evolved convergently in Gnetum, enabling faster flow via reduced resistance.
Cycas/Zamia/Ginkgo retain primitive tracheid-only systems with bordered pits.
Correct Answer: 4. Gnetum
Gnetum stems/roots contain true vessels alongside tracheids; protoxylem spiral/annular, metaxylem with circular bordered pits.
Secondary growth features successive cambial rings producing vessel-rich wood; unique among gymnosperms.
Option Breakdown
| Option | Xylem Composition | Vessels? | Explanation |
|---|---|---|---|
| 1. Cycas | Tracheids only; no vessels | No | Cycadales: primitive tracheids, girdling leaf traces. |
| 2. Zamia | Tracheids only; no vessels | No | Cycad like Cycas; endarch bundles, no perforation plates. |
| 3. Ginkgo | Tracheids only; no vessels | No | Ginkgoales: eustele, spiral protoxylem; vessel-less. |
| 4. Gnetum | Tracheids + vessels | Yes | Gnetales: advanced xylem with perforation plates. |
Evolutionary Significance
Vessel presence in Gnetum supports gymnosperm-angiosperm affinity hypotheses (e.g., Gnetifer theory).
Enhances hydraulic conductivity; Gnetum often vine-like in tropics.
