Scadoxus is a genus of African and Arabian plants in the Amaryllis family, subfamily Amaryllidoideae.[2] The English names blood lily or blood flower are used for some of the species. The genus has close affinities with Haemanthus. Species of Scadoxus are grown as ornamental plants for their brilliantly coloured flowers, either in containers or in the ground in frost-free climates. Although some species have been used in traditional medicine, they contain poisonous alkaloids.
Species of Scadoxus grow from bulbs or rhizomes. Bulbous species usually also have distinct rhizomes. Particularly in the non-bulbous species, the petioles (leaf stalks) overlap to produce a false stem or pseudostem, which may be purple-spotted. The leaf blades are lanceolate to ovate with a thickened midrib. The leafless flowering stem (scape) is also sometimes purple-spotted, and either appears from among the leaves or pushes through the side of the pseudostem.[3][4]
The flowers are borne at the top of the scape in the form of a many-flowered umbel. Four or more bracts are present under the umbel at first. In some species, such as Scadoxus membranaceus, these bracts persist during flowering; in other species they wither before the flowers are fully open. Individual flowers have six red to pink tepals, joined at the base to form a tube. In most species, the flowers are more-or-less upright, although in Scadoxus cyrtanthiflorus the open flowers droop and in Scadoxus nutans the top of the scape bends over so that the flowers face downwards. The filaments of the stamens arise from the base of the tepals and may be flattened. The fruit takes the form of a globose berry, orange to red when ripe.[3][5]
The genus was given its name in 1838 by Constantine Samuel Rafinesque. The precise etymology of the name as a whole is unclear. Rafinesque glossed the name as "umb. glor."[6] (possibly meaning umbella gloriosa, "glorious umbel"). Doxus, meaning "glory" or "splendour" in Greek, is usually interpreted as a reference to the often scarlet flowers of the genus.[7] The prefix sca may be derived from the Greek skia meaning "shade"[8] (sciadon is the Greek equivalent of the Latin umbella, "umbrella",used of flower heads in the form of umbels[9]).[10]
Scadoxus is placed in tribe Haemantheae within the subfamily Amaryllidoideae, a tribe reserved for genera with fruit in the form of berries (baccate fruit). The tribe is predominantly African in origin and comprises six genera: Apodolirion, Gethyllis, Haemanthus, Scadoxus, Clivia and Cryptostephanus. The single most parsimonious phylogenetic tree found by analysis of both nuclear and plastid DNA in a 2004 study showed that Scadoxus is most closely related to Haemanthus:[11]
Scadoxus was originally separated from Haemanthus by Rafinesque in 1838.[6] His type species, Scadoxus multiflorus, had been described as Haemanthus multiflorus by Thomas Martyn in 1795.[12] This separation was ignored by most workers until 1976, when Scadoxus was recognised as a distinct genus by Ib Friis and Inger Nordal. Haemanthus species are southern in distribution, form true bulbs and have 2n = 16 chromosomes, whereas Scadoxus species are found throughout tropical Africa, do not all form bulbs and have 2n = 18 chromosomes.[11] The leaves of the two genera are also different. The leaves of Scadoxus species are thin, spirally arranged, with a distinct stalk (petiole); in some species their bases form a pseudostem. The leaves of Haemanthus species are thicker, opposite, without a distinct petiole, and never form a pseudostem.[13]