Hecastocleis

The leaves are alternately set along the branches. The leaf blades are hairless or with a few soft hairs, slightly olive green, stiff and leathery, with three main veins, linear to narrowly ovate in shape, 1–4 cm (0.39–1.57 in) long, their base approximately clasping the branch, with thickened margins usually carrying three to six spines of 1–3 mm (0.039–0.118 in) long, denser spaced near the base, while the tip is more or less abruptly tapering into a point.[1]

The complex inflorescences are carried at the end of the branches. These consist of a number of crowded clusters. Each of the clusters is subtended by white to yellowish green, wavy, ovate to orbicular bracts that have a spiny margin, and further consist of one to five flower heads which each contain only a single disk floret. The most outward part of the flower head is the involucre, which is narrowly vase-shaped to cylindric and approximately 1 cm (0.39 in) high, and consists of about six worls of four bracts called phyllaries, which have often soft woolly hairs around the edge. The base of the flower head (or receptacle) is flat and lacks a bract directly at the base of the floret. The corolla of the florets is pinkish purple when still in bud, but turns pinkish white at flowering, at which time it is about 1 cm (0.39 in) high. These are hermaphrodite, star-symmetric (or actinomorphic), and have five narrow outwards oriented lobes. The five pinkish purple anthers are fused into a long tube, that initially covers the entire style. The bone-colored style grows through the anther tube, collecting the pollen on hairs, and displaying it above the anter tube like in all other Asteraceae. The style branches are only 0.1–0.5 mm (0.0039–0.0197 in) and have rounded tips. At the base of the corolla the one-seeded indehiscent fruit (called cypselas) develops, which is not flattened, has four to five hardly visible nerves, turns brown and has lost any hairs when ripe, and is about ½ cm (0.2 in) high. On the top of the cypselas is a crown of six unequal scales (the pappus) of 1–2 mm (0.039–0.079 in) high. These scales are lanceolate in shape, may have several teeth and are sometimes fused at their base, so forming a crown. The pollen of Hecastocleis is yellow, unadorned and tricolpate.[1]

Scholars agree that Hecastocleis occupies a very isolated position on the evolutionary grade of subfamilies of the Asteraceae, and this is expressed by the erection of the monotypic subfamily Hecastocleidoideae.[2]

The current insights in the relationships between Hecastocleis and its closest relatives, as based on genetic analysis, is expressed in the following tree.

Earlier splits of the Asteraceae tree are supposed to have taken place in southern South America. The splits that occur later than Hecastocleis have occurred Africa, especially southern Africa, and some may also have occurred in Asia. This implies that the common ancestor of Hecastocleis and all later branches moved from South America to North American and after the split with Hecastocleis, the ancestor of the remainder of the subfamilies arrived in Africa from North-America. Alternatively, only the ancestor of Hecastocleis migrated from South America to North America while the ancestor of the remainder was distributed from South America to Africa. The placement of Hecastocleis in the tree could also be incorrect due to parallel evolution an reversal of earlier mutations. However, the support in the analysis for the separation of Hecastocleis from the Gochnatieae is strong.[1]

The name of the genus Hecastocleis is the contraction of two Greek words, ἕκαστος (hekastos) meaning "each" and κλειω (kleio) which is said to mean "to shut up", referring to each flower having its own involucre. An alternative meaning of kleio is "glory". The species was named shockleyi in honor of William Hillman Shockley, an early plant collector of the flora of Nevada and father of the co-inventor of the transistor William Shockley.[1]