Q.57 Which of the following is not an identifying feature of Cycas
1. Antherozoids are motile
2. Anatomical features of the leaflet indicating it as a mesophyte
3. Circinate venation of the foliage leaves
4. Xylem lacking vessels
Cycas exhibits several distinctive gymnosperm features, but one option does not identify it correctly. The correct answer is option 2.
Correct Answer
Option 2: Anatomical features of the leaflet indicating it as a mesophyte
Cycas leaflets show xerophytic adaptations like thick cuticle, sunken stomata, and sclerenchyma, not mesophytic traits such as thin cuticle and large intercellular spaces.
Option Explanations
1. Antherozoids are motile
Cycas produces multiflagellate, spirally coiled antherozoids, a primitive gymnosperm trait enabling swimming in syrupy pollination drops for fertilization.
2. Anatomical features of the leaflet indicating it as a mesophyte (Not a feature)
Leaflets have hypodermal sclerenchyma, thick hypodermis, sunken stomata in grooves, and revolute margins (e.g., Cycas revoluta), indicating xerophyte adaptations for arid habitats, not mesophyte water-efficiency traits.
3. Circinate venation of the foliage leaves
Young pinnate leaves show circinate vernation (apex-coiled), a characteristic of Cycadales, with leaflets uncoiling as they mature; venation is parallel without midribs in some species.
4. Xylem lacking vessels
Cycas xylem is tracheidary only, without vessels (a pteridophyte/early gymnosperm feature), featuring annular spiral thickenings and secondary growth via cambium.
Option Analysis
| Option | Feature Description | Identifies Cycas? | Reason |
|---|---|---|---|
| 1 | Antherozoids are motile | Yes | Multiflagellate sperm unique to cycads among gymnosperms. |
| 2 | Mesophyte leaflet anatomy | No | Xerophytic, not mesophytic; thick-walled cells, sunken stomata. |
| 3 | Circinate venation | Yes | Ptyxis in young leaves diagnostic for Cycadales. |
| 4 | Xylem lacking vessels | Yes | Primitive tracheids only, no conducting vessels. |
