Phytochrome is found in

The correct option is Flowering plants.

Phytochromes are a class of photoreceptor proteins found in plants, bacteria, and fungi, which are used to detect light. They are particularly sensitive to light in the red and far-red regions of the visible spectrum.
In plants, phytochromes regulate many aspects of development. They are crucial for photomorphogenesis, which is the process by which plants grow and develop in response to light signals. This includes processes such as seed germination, seedling elongation, the synthesis of chlorophyll, and the timing of flowering based on day length (photoperiodism).

Among the given options, phytochromes are most prominently characterized and widely distributed in flowering plants (angiosperms), where they play a fundamental role in regulating their life cycle, especially transition to flowering and photomorphogenic development.