Leucospermum
Leucospermum commonly known as pincushions, is a genus of evergreen upright, sometimes creeping shrubs that is assigned to the Proteaceae, with currently 48 known species.
The shrubs mostly have a single stem at their base, but some species sprout from an underground rootstock, from which the plant can regrow after fire has killed the above ground biomass. In a larger group of species, specimens are killed by fire, and their survival depends on the seeds. In all species, seeds are collected by ants, which take them to their underground nests to feed on their ant breads, a seed dispersal strategy known as myrmecochory. This ensures that the seeds do not burn, so new plants can grow from them.
Leucospermum species mostly have seated, simple, mostly leathery, often softly hairy leaves, set in a spiral, with entire margins or more often, with 3–17 blunt teeth with thickened, bony tips, and without stipules at their foot. The flowers are organised with many together in heads with bracts on the under- or outside. The hermaphrodite flowers themselves are set on a common base that may be cylindrical, conical or flat, and have small bracts at their base. The flowers have a perianth that is hairy on the outside, particularly at the tip, and consists of four tepals that are merged into a tube. Usually the four anthers are merged individually with the tip the perianth lobes, and only in a few species, a very short filament is present that further down cannot be distinguished from the tepals anymore. While still in the bud, the pollen is transferred from the anthers to the pollen-presenter, a thickening at the tip of the style. At that stage, the style grows considerably and rips through the sutures between the two perianth lobes facing away from the centre of the flower head. The perianth lobes all four remain attached to each other, or with three, or the four free lobes all curl back on themselves, rimming the top of the tube. The superior ovary consists of one carpel and contains a single ovary, and is subtended by four small scales. The fruit is an oval or almost globe-shaped nut.
Most species have very limited ecological ranges and distribution areas, and many are rare or endangered. The often attractive, large flower heads and evergreen foliage, the straight stems, combined with long flowering period makes that Leucospermum species and their hybrids are bred as garden ornamental and cut flower.
Description
Most pincushions are upright shrubs or even small trees of high, that usually have a single main stem. Some species however only have trailing branches and can form low mats, in diameter. Yet another set of species grow several stems directly from a rootstock in the ground. This is an important character in distinguishing between some species. Dried specimens of L. pedunculatum and L. prostratum can be difficult to distinguish, but although both are prostrate species, the growth habits in the field differ considerably. In L. pedunculatum many horizontally spreading branches develop from an about main stem, in L. prostratum the branches rise from an underground woody rootstock. The leaves are alternately set along the stem, distanced and slightly pointing towards the tip of the branch or overlapping, mostly without, sometimes with a leaf stalk but always without stipules at their base, long and linear, elliptic, oblanceolate, oval, inverted egg-shaped or spade-shaped, the edge entire or with up to 17 teeth towards the tip, hairless or with a covering of soft cringy one-celled hairs, sometime interspersed with longer straight silky hairs.The flower heads are seated or have a short stalk, and grow individually in species with large heads or with two to ten together in species with smaller heads, in the axils of the leaves near the end of the branches. The general shape of the heads is a flattened, round, egg- or cone-shaped sphere of in diameter. The position not at the very tip of the branches helps to distinguish Leucospermum from related genera such as Diastella, while the more than one head per branch helps to distinguish the sections Diastelloides and Hamatum from the other sections. The involucral bracts are green in fresh specimens, and inconspicuous. They may have different shapes such as linear or ovate, with a sharp or pointed tip. In the majority of the species the involucral bracts have tough rubbery consistency and are usually softly hairy, overlapping and tightly pressed against the flower head. L. parile, L. tottum and L. vestitum on the other hand have thin, papery bracts. The common base of the flowers that jointly constitute a single flowerhead varies considerably among species. It may be flat, globe-shaped, pointy conical or blunt cylindric. This character can best be seen by cutting a flower head lengthwise in two equal halves.
The individual flowers are subtended by a bract that is wooly at its foot and softly hairy or hairless near the tip. Sometimes it grows on while the flower is in bloom and eventually becomes woody. While still in the bud, the perianth is a tube of long. When flowering, the perianth is yellow, orange, crimson, pink or white in color, straight or often curved towards the center of the flower head. The perianth consists of four tepals that are fused into a tube of either of uniform width or expanding towards the tip, but there are also a few species where it is inflated nearer the tip, such as in L. utriculosum, L. hamatum and L. harpagonatum. Above the tube, three of the lobes may become fused in a sheath, open towards the outside of the flower head, while the lobe facing the rim of the flower head is free. In the upper part of the perianth all four lobes may remain fused or only the three that remained already fused in the middle part. In the section Diastelloidea all four lobes are free in the upper parts and curl back forming a four-part rim around the top of the tube. The anthers differ little between species of Leucospermum and are usually fused with the tips of the perianth lobes, and filaments cannot be identified, but in the species that constitute the section Brevifilamentum, a filament of long makes the connection between the anther and the lobe. The buds are ripped open along a suture facing away from the center of the flower head by the style that grows in length quickly, eventually reaching a length of, straight or with a curve towards the center of the flower head, in diameter, often narrower nearer to the tip or thread-shaped, mostly identically colored as the perianth. The end of the style is thickened and holds the pollen that is transferred there just before the bud rips open. There is a considerable morphological variation in this so-called pollen presenter between species. The pollen presenter may be cylindric, oval, or conic in shape, either or not split in two lobes near the tip or oblique. The very tip has a groove that functions as the stigma that is centrally or oblique oriented. The finely powdery ovary is long, and gradually merges into the style base. It consists of one carpel and contains a single pendulous ovule. At the base of the ovary are four linear or awl-shaped scales of long that secrete a copious amount of nectar.
The indehiscent fruit consists of one cavity, containing one oval to globe-shaped seed of long, with a broad indent where it was attached, hairless or covered with a fine powder and generally partially covered by a pale elaiosome.
The sixteen Leucospermum species that have been analysed are all diploids having twelve sets of homologue chromosomes, which is consistent with the rest of the subtribe Proteinae.