**Cephaleuros, which causes Red rust of tea is a Green Algae.**

**Explanation:**

Cephaleuros is a genus of parasitic green algae that belongs to the family Trentepohliaceae. It is responsible for causing a plant disease known as red rust or algal leaf spot in tea plants, which affects the leaves and stems.

**Characteristics of Cephaleuros:**

Cephaleuros is a unicellular organism that can be observed as a thin, reddish to purplish layer on the surface of tea leaves and stems. It has the following characteristics:

1. **Pigmentation:** Cephaleuros appears red or purple in color due to the presence of pigments such as chlorophyll a, chlorophyll b, and beta-carotene.

2. **Cell Structure:** It has a simple cell structure and lacks any specialized organs or tissues.

3. **Mode of Nutrition:** Cephaleuros is an autotrophic organism, meaning it can produce its own food through photosynthesis. It obtains energy from sunlight and nutrients from the host plant.

4. **Reproduction:** It reproduces asexually by forming spores called zoospores. These zoospores are released into the environment and can infect nearby tea plants, leading to the spread of the disease.

**Red Rust or Algal Leaf Spot:**

Red rust, also known as algal leaf spot, is a plant disease caused by the parasitic green algae Cephaleuros. It primarily affects tea plants but can also infect other plants such as coffee, citrus, and ornamental plants. The disease manifests as reddish or purplish lesions on the leaves and stems of the infected plant.

**Effects of Cephaleuros on Tea Plants:**

1. **Reduced Photosynthesis:** The presence of Cephaleuros on the leaves and stems of tea plants can obstruct sunlight and reduce the plant's ability to perform photosynthesis effectively. This can lead to a decrease in plant growth and productivity.

2. **Weakening of Plant:** As Cephaleuros continues to infect and spread within the plant, it weakens the overall health of the tea plant. This can make the plant more susceptible to other diseases and pests.

3. **Aesthetic Damage:** The reddish or purplish lesions caused by Cephaleuros can also lead to aesthetic damage, making the tea plant less visually appealing.

**Control Measures:**

To control Cephaleuros infection in tea plants, the following measures can be taken:

1. **Pruning and Sanitation:** Infected plant parts should be pruned and properly disposed of to prevent the spread of the disease.

2. **Chemical Control:** Fungicides or algaecides specifically formulated for controlling Cephaleuros can be applied to the tea plants. These chemicals should be used as per the recommended dosage and frequency.

3. **Cultural Practices:** Proper cultural practices such as maintaining good plant hygiene, ensuring adequate sunlight and air circulation, and providing balanced nutrition can help prevent and manage Cephaleuros infection.

In conclusion, Cephaleuros is a green algae that causes red rust or algal leaf spot in tea plants. It is a parasitic organism that weakens the tea plant by obstructing photosynthesis and can be controlled through pruning, chemical control, and proper cultural practices.