Encephalartos altensteinii is a medium to large plant with stems up to 5 meters long and a diameter of 35cm. Stems can be erect or reclining and grow in clumps or as single stem plants. Suckers are formed from the base.
Young leaves are bright green and covered with hair. Leaves can be 1-3 meters long, 20-30cm wide and more or less flat in cross section with a straight profile. Colour is bright yellowish green and the petiole is 10-30cm long.
The pinnae are lanceolate and moderately spaced along the rachis. Lower pinnae are reduced, but not to spines. Median pinnae are 10-15cm long and 2-3cm wide. They are rigid, pungent-tipped and normally entire but can have 1-5 teeth on the margins.
Pollen and seed cones are markedly dissimilar and occur 2 to 5 on a stem. Male cones are 40-50cm long, 12-15cm in diameter and cylindrical but tapered to the top. Colour is yellow to yellowish green. Peduncle is sturdy and can be 5-10cm long. Female cones are 40-55cm x 25-30cm, sessile, oblong-ovoid and yellow with brown hair. Seeds are 3.5-4cm x 2-2.5cm and bright red.
E. altensteinii was first described in 1834. This species is well known and common in private collections because it propagates easily and grows relatively fast. A specimen of E. altensteinii (see E. longifolius) sent to Kew Gardens in 1775 is still growing in the Palm House. This species is very robust and cases exist of plants growing vigorously after being replanted, after years in a shed.
This species is variable and plants from the eastern localities have less spiny pinnae. E. altensteinii is closely related to E. natalensis but it can be distinguished by the absence of reduced, spiny pinnae on the petiole. Natural hybrids with E. trispinosus are known where these species grow close to each other. Natural hybrids have also been recorded with E. villosus, E. arenarius and E. latifrons. The hybrids usually have intermediate characteristics between the parents.