Description from Flora of China
Crassula mongolica Franchet, Nouv. Arch. Mus. Hist. Nat., sér. 2, 6: 16. 1883.
Herbs 2.5-5 cm tall, glabrous. Stems branched from middle, ascending. Leaf blade lanceolate, 2-3 mm, apex often reflexed. Flowers axillary, 4-merous; pedicel longer than sepals in fruiting material. Sepals erect, violet striate adaxially, lanceolate, apex obtuse. Petals brown striate, shorter than sepals, base connate, apex hooded. Stamens with anthers ovoid. Nectar scales broadly obconical, ca. 1/4 as long as carpels. Styles shortly acuminate. Follicles gibbous, 7- or 8-seeded. Seeds yellow, cylindric-ovoid, densely rounded tuberculate.
This species needs comparison with Tillaea decumbens (Thunberg) Willdenow, which was originally described from S Africa but is now known to be adventive elsewhere.
* Edges of ponds. NE Hebei (Chengde).