Clerodendrum is a genus of flowering plants formerly placed in the family Verbenaceae, but now considered to belong to the Lamiaceae (mint) family. Its common names include glorybower, bagflower and bleeding-heart. It is currently classified in the subfamily Ajugoideae, being one of several genera transferred from Verbenaceae to Lamiaceae in the 1990s, based on phylogenetic analysis of morphological and molecular data.
Estimates of the number of species in Clerodendrum vary widely, from about 150 to about 450. This is partly because about 30 species have been transferred to Rotheca, about 30 more to Volkameria, and 1 to Ovieda. The type species for the genus is Clerodendrum infortunatum. It is native to Sri Lanka and the Andaman Islands.
The genus is native to tropical and warm temperate regions of the world, with most of the species occurring in tropical Africa and southern Asia, but with a few in the tropical Americas and northern Australasia, and a few extending north into the temperate zone in eastern Asia.
They are shrubs, lianas, and small trees, usually growing to tall, with opposite or whorled leaves. C. floribundum can grow to tall. Clerodendrum fistulosum and Clerodendrum myrmecophila have hollow stems that are inhabited by ants. Clerodendrum trichotomum is a common ornamental in warmer parts of the world. Eight other species are also grown in the tropics for their abundant and attractive flowers. One of these, Clerodendrum macrostegium, suckers abundantly from the roots, often producing a thicket within a few years.
The following species are cultivated in the UK: C. chinense C. splendens C. thomsoniae C. trichotomum
Clerodendrum species are used as food plants by the larvae of some Lepidoptera species including Endoclita malabaricus and Endoclita sericeus. Both butterflies and hummingbirds are often attracted to blooming clerodendrum.
Description
The following description is based on the one by Yuan et alii (2010) and applies to only the monophyletic circumscription of Clerodendrum.
Clerodendrum is a genus of small trees, shrubs, lianas, and subherbaceous perennials. Leaves decussate or whorled, never spiny as in some close relatives.
Inflorescence usually terminal. Sepals usually connate, often colored, usually accrescent. Corolla red to yellow, pink, or white. Corolla tube 5-lobed, the lobes usually unequal.
Stamens 4 (rarely 5), usually in 2 pairs of unequal length and projecting well beyond the mouth of the corolla.
Ovary incompletely 4-locular. Ovules 4. Style terminal on the ovary, bifid.
Fruit a drupe, usually with 4 grooves or lobes, 4-seeded (rarely 2-seeded by abortion).
Pollination
Clerodendrum and its relatives have an unusual pollination syndrome which avoids self-pollination. This mating system combines dichogamy and herkogamy.
The flowers are protandrous. When the flower opens, the stamens stand erect, parallel to the central axis of the flower, while the style bends over, holding the stigma beyond the rim of the corolla. After the pollen is shed, the stamens curl up or bend over, and the style straightens out, bringing the stigma to the center of the flower. Except for Aegiphila, which is heterostylous, this breeding strategy is shared by all members of the clade consisting of Kalaharia, Clerodendrum, Volkameria, Aegiphila, Ovieda, Tetraclea, and Amasonia.
History
Clerodendrum was named by Linnaeus in Species Plantarum in 1753. The name is derived from two Greek words, kleros, meaning "chance or fate" or "clergy", and dendron, "a tree". It refers to the considerable variation in reports of the usefulness of Clerodendrum in medicine, and also to the fact the trees were used for religious purposes in Asia.
Regional revisions of Clerodendrum have been done for local floras, but the last monograph of the entire genus was by John Isaac Briquet in 1895. He recognized about 90 species, defining the genus broadly to include species that others had placed in Rotheca, Volkameria, and Ovieda. His circumscription was followed by most authors for the next 100 years, even though it was widely believed to be problematic.
In 1997, phylogenetic analysis of DNA data showed that Clerodendrum, as then understood, was polyphyletic. This situation was remedied in 1998 with the revival of Rotheca. This taxonomic change was based on previous work and on a molecular phylogenetic study that was not published until the following year.