Common hedge parsley (Torilis arvensis) and poison hemlock (Conium maculatum) are both plants that can be easily confused due to their similar appearances. Here are some distinguishing features that can help in identification:

1. Stems
   - Hemlock has smooth, hollow stems with purple blotches. 
   - Hedge parsley, on the other hand, has hairy stems without any blotches.

2. Leaves
   - Hemlock leaves are fern-like, finely divided, and have a musty smell when crushed.
   - Hedge parsley leaves are also finely divided but usually have a lighter green color and do not have a musty odor.

3. Flowers
   - Both plants have small white flowers arranged in umbrella-like clusters, which is a common characteristic of the Apiaceae family. However, the flower clusters of hedge parsley are typically less dense than those of hemlock.

4. Fruit
   - Hedge parsley produces small, prickly fruits, whereas hemlock's fruits are smooth and ridged.

5. Height
   - Hemlock can grow much taller, often reaching up to 2-2.5 meters in height, while hedge parsley usually grows up to 1 meter.

6. Habitat
   - Hemlock often grows in damp, poorly drained soils like riverbanks and ditches, whereas hedge parsley is typically found in dry, disturbed sites like roadsides and fields.

Remember, it's crucial to correctly identify these plants since poison hemlock is extremely toxic and can be fatal if ingested or absorbed through the skin. When in doubt, consult a local botanist or use a reputable plant identification guide or app.