Xerophyte

Central Spines

1-5 (mostly 3), stout, yellowish to greyish, 1-5 cm long.

Seeds

Bright black, numerous.

Description

Cephalophorus senilisSN|6897]]SN|6897]] is a columnar and erect cactus 6 to 10 or even 15 meters high, simple or branching only basally. The flowering areoles develop an abundance of wool which confluently forms a dense mass called a pseudocephalium at the top or on one side near the top. The flowers are nocturnal red, yellow, or white, though the plant may not flower until 10–20 years old. The fruit usually are obovoid. The most striking feature is the shaggy coat of long, white silky hairs suggestive of unkempt hair on an old man and hence the name old man cactus, and similar names. The coat is a particularly striking silvery white on the young cactus; as the plant ages the stem begins to lose its covering. The hairs are modified spines and they make many a plant appear almost snow-white; they serve to protect the plant from frost and sun. However, the hairs are only the radial spines of the cactus; they conceal formidable sharp yellow central spines that belie the inoffensive appearance of the hairy covering.

Cephalium

Developing on plants when about 6 meters high, broadening above, at first confined to one side but later encircling the top of the plant. The flowering zone in the lateral cephalium is characterized by its interareolar space reduction, areole size increment, and high production of long bristles and woolly hairs in the areoles (The bristles of the pseudocephalium are dense, white, twice as long as the wool). Moreover epidermis lacks of chlorenchyma (photosynthetic tissue) . The lateral cephalium of C. senilis shows modifications previously reported for the Espostoa species with lateral cephalium.

Flowers

The flowers are nocturnal, solitary and grow one by one. Funnel shaped, including the ovary, 5-9 cm long, 7-8 cm in diameter, yellowish pink to rose-coloured. Pericarpels and floral tubes hairy with few scales.

Stem

Cylindrical, columnar, light to bright green, becoming grey, to 30 cm in diameter, sometime branched from the base, top rounded. The individual stems are usually unbranched, being unable to withstand the weight of side branches adequately. The ribs are numerous (20-30), low, slightly notched. Very little wood-tissue is developed and the largest individuals can easily be cut down with a pick or small knife. This species undergoes profound changes in the upper parts of the trunk at maturity (about 15 years). Tissues from that part change to originate an area specializing in the production of flowers (lateral cephalium or pseudocephalium).

Fruits

The fruits develops three to four weeks after anthesis (flowering), they are, obovoid, 2.5 to 3 cm long, rose-colored, capped by the chartaceous base of the flower. The pericarpel and flower-tube bears a few minute scales with hairs in their axils. The perianth persists on the ripening fruit. The fruits remain connected to the pseudocephalium and seeds dispersion is carried out bybirds.

Areoles

7 mm long by 5 mm wide, closely set (12 to 14 mm apart); the ones at base of old plants producing 20-30 weak, hairlike, white or greysh bristles (modified radial spines) 6-14 cm long, the ones in the pseudocephalium producing similar but shorter bristles intermixed with dense, tawny wool, 4 to 6 cm long.