Schiedea lydgatei is a shrub that grows 10–100 cm tall with erect to sprawling stems that are terete, 4-angled or ridged, glabrous, and often have many short lateral branches. The stems are green to greenish-purple with internodes 0.5–7.5 cm long, while older branches exhibit tan bark. The leaves are simple and opposite, elliptic to broadly elliptic, elliptic-ovate, or elliptic-lanceolate, measuring 2–5 cm in length and 0.6–1.7 cm in width. Leaf apices are acuminate and mucronate, and bases are cuneate, frequently connate around the stem. The thinly coriaceous blades are pale yellowish-green, occasionally glaucous and reflective, with entire, slightly thickened, and weakly revolute margins. Each leaf typically exhibits three principal veins, with the central vein being the most pronounced. Petioles measure 0.4–0.6 cm long, and stipules are absent. The inflorescence is terminal, diffuse, and measures 10–25 cm long, bearing 7–109 bisexual flowers. Inflorescence bracts along the central axis are 2–6 mm long, while those on branches and flowers are smaller (2–2.5 mm), green to purple-tinged, and subulate. Pedicels are notably quadrangular, conspicuously flattened and grooved, measuring (8–)10–18(–20) mm long. Flowers have no petals but bear narrowly ovate sepals 4–4.7 mm long, oriented at 45° to 80° relative to the pedicel, green or tinged purple, and opaque with pale veins. Sepals are reflexed, glabrous, and display scarious, sometimes irregularly undulate margins. Stamens number 10, with dimorphic filaments; the antisepalous filaments are slightly longer (5.5–5.6 mm) than the alternate ones (4.9–5.2 mm), and all have yellow anthers (0.7–0.9 mm). The superior ovary is single-celled, with free-central placentation, and typically has three green styles. The fruits are ovoid capsules 4–5.5 mm long. Seeds are orbicular, approximately 0.8 mm in length, with rugose faces and papillose margins, containing starchy perisperm but lacking true endosperm. It is found in dry shrubland habitats between 600-955 meters.