Sickle-leaved Cymodocea

Thalassodendron ciliatum, commonly known as the sickle-leaved cymodocea, is a species within the Thalassodendron genus of seagrasses, which is part of the Cymodoceaceae family.

This species exhibits a broad distribution across the Indo-Pacific region, though its abundance varies throughout this range. Thalassodendron ciliatum has been documented from the western 🇵🇭 Philippines to Borneo, 🇸🇬 Singapore, 🇮🇩 Indonesia, Papua 🇵🇬 New Guinea, the Caroline Islands, 🇻🇺 Vanuatu, 🇦🇺 Australia, 🇮🇳 India, and the 🇲🇻 Maldives. In addition, it is prevalent from the 🌊 Gulf of Oman to the 🌊 Red Sea, extending to 🇿🇦 South Africa, 🇲🇬 Madagascar, the 🇸🇨 Seychelles, the Comoros, the Mascarene Islands, and certain areas of Malesia and the 🇸🇧 Solomon Islands.

Thalassodendron ciliatum typically inhabits the upper portion of the sublittoral zone, extending to depths of up to 17 meters. In deeper locations, it forms dense monospecific meadows on sandy substrates, coral reefs, and sand-covered rocks. Although fast-growing, this seagrass species is slow to re-colonize and is susceptible to intense grazing by sea urchins. It is also vulnerable to anthropogenic pressures, such as coastal development, pollution, eutrophication, seaweed farming, beach seines, and drag net trawling.

The leaves of Thalassodendron ciliatum are linear and falcate, often exhibiting a red or red-striped appearance. They typically measure 10–15 cm in length and 6–13 mm in width, with an average width of 10 mm. The leaf margins are primarily entire, with serrations evident towards the tip. The leaf sheath is wide and compressed, measuring 15–30 mm in length, and generally appears pink.

The species features a thick, well-developed rhizome, up to 0.5 cm in thickness, with mats formed by the rhizome approximately 5–10 cm thick. Each fourth internode along the rhizome generally hosts one to two stems. The primary stem is either unbranched or slightly branched, ranging from 10 to 65 cm in length, while the secondary stem, if present, is typically under-developed, manifesting as a bud. The roots occur in groups of one to five, varying from slightly to highly branched, and are located at the internode preceding the stem.