Crassula pellucida is a very variable species and has five recognised subspecies. Three of them are endemic, the other two are also found in neighbouring countries in southern Africa and into tropical Africa.

Subspecies pellucida, western trailing crassula, has hairless branches. The leaves with a petiole (petiolate) or without a petiole (sessile), the opposite leaf blades are free, obovate to broadly elliptic, blunt tipped (obtuse) or tipped with a short point (apiculate), margins are irregularly papillose (small, pimple-like protuberances). The flowerhead is usually a terminal dichasium (each flowering stem gives rise to two lateral flowering stems on either side), and occasionally a single flower is produced. The calyx is about two thirds as long to as long as the corolla. Flowering is in spring to midsummer (Nov. to Feb.). It occurs in the Western Cape and Eastern Cape, from the Winterhoek Mountains, to the Cape Peninsula to the Swartberg Mountains and near Swellendam, usually on rock outcrops in shaded, moist places or in forests.

Subspecies alsinoides, northern or single-flowered trailing crassula, produces a single, star-shaped white flower in the axil of a leaf. Flowering is in spring and summer (Oct. to Mar.). Leaves are sessile, ovate to lanceolate-spathulate, taper to a point (acute), with a sharp point, margins with elongate papillae making them appear minutely dentate (serrulate). Internodes hairy. It occurs in the northern parts of South Africa, mainly in Limpopo and Mpumalanga and rarely in Eastern Cape, KwaZulu-Natal, and is widespread and common in tropical Africa, in moist shaded places, often in forests along streams or in swamps.

Subspecies brachypetala, common or short-petalled trailing crassula, has hairy internodes at least along a line on either side of the stem. Leaves are sessile to petiolate, lanceolate to ovate, acute, cuneate, with irregularly spreading pappillae along the margins. The inflorescence is a terminal dichasium, the pedicels are hairy. The calyx is as long as or longer than the petals. Flowering is during summer (Dec. to Apr.). It is a common, widespread and variable species that occurs in Eastern Cape, Free State, KwaZulu-Natal, Limpopo and Mpumalanga and in tropical Africa, in moist areas in grassveld, forest margins, often on rocky outcrops.

Subspecies marginalis, eastern or fused-leaf trailing crassula, has hairless branches. The leaves are sessile, with the blades of opposite leaves being fused to one another to form a disc up to 10 mm in diameter. Its leaves are broadly ovate, with a pointed apex and a horny margin without papillae. The inflorescence is 1 to 3 terminal dichasia, often appearing umbellate, and pedicels are not hairy. The calyx is usually about half as long as the corolla. Flowering is in spring and early summer (Sep. to Dec.). It occurs along the southeastern coast of South Africa, in Eastern Cape, from George to East London, usually on rock outcrops, in shaded, moist places or in forest.

Subspecies spongiosa, Bokkeveld or spongy trailing crassula, is a hairless, decumbent annual that occurs on the Bokkeveld Escarpment between Nieuwoudtville and Calvinia, growing in sandy soil in sheltered kloofs. Leaves elliptic, often with a colourless point at the tip. Fowering is in spring (Oct. to Nov.) and the calyx, carpels and receptacle become spongy after flowering.