Aponogeton stuhlmannii Engl.

Plants monoecious.. Tuber globular to conical, 6–12 mm. long and 4–10 mm. in diameter, with very numerous whitish slender roots.. Leaves usually 5–10 per tuber; petiole 5–20 cm. long and 0.2–0.6 mm. thick; blade narrowly oblong to lanceolate, 2–5 cm. long and 4–10 mm. wide, with 5–9 parallel lateral nerves, floating on the surface of the water; base cuneate to truncate, tip obtuse; primary leaves occasionally produced, 1–2 cm. long, linear, without blade.. Flowers white, often drying a bluish white, rather laxly set on unbranched somewhat unilateral spikes on slender peduncles; peduncles 5–15 cm. long and 1–1.5 mm. thick above, green but inflorescence-axis and base white; spathe 6–10 mm. long, greenish, usually early caducous.. Spike 1–2 cm. long and 5–10 mm. wide with tepals spreading, the flowers usually inserted on one side of the axis, but at maturity often more cylindrical, only 7–15-flowered.. Tepals 2, white and shiny, but often with a lilac tinge, ligulate, 3.5–5.5 mm. long and 1–2 mm. wide, 1-nerved.. Stamens 6; filaments 2–2.5 mm. long, lilac but whitish near the thicker base; anthers 0.5–0.6 mm. long and 0.3–0.4 mm. wide, brownish yellow, but turning black when withering.. Ovaries 2–4, green with 2–10 ovules.. Follicles green to somewhat bluish (but beak whitish at least near die tip), 2–3 mm. long, including a ± 1 mm. long curved beak, and 0.5–0.6 mm. wide.. Seeds elliptic, 1.5–2.5 mm. long and ± 0.5 mm. wide, with a double testa, not longitudinally ridged.