Lepidagathis Willd.

Kameyama, C. (2008). New species, nomenclatural changes and lectotypifications in Neotropical Lepidagathis Willd. (Acanthaceae). Kew Bulletin 63: 565. https://doi.org/10.1007/s12225-008-9066-2

Morphology General Habit

Species of Lepidagathis are small decumbent or erect subshrubs, or erect to sprawling shrubs. Decumbent subshrubs usually have adventitious roots at the nodes that touch the substrate. Some erect unbranched subshrubs are hemicryptophytes; they have a short, thick, partially underground shoot with cataphylls from which grow adventitious roots and aerial shoots. These aerial branches are annual and die after flowering and fruiting.

Morphology Leaves

The leaves, as in many Acanthaceae, are decussate and in most of the species evidently anisophyllous (leaves born at the same node having different sizes). This feature is also present in many unrelated species of Acanthaceae (Brummit 1989; Manktelow 1996). In some species differentiated leaves also occur at the base of the stem or close to the inflorescences. The leaves near the main florescence can be different from the others in shape and venation pattern and usually are intermediate between normal leaves and bracts.

Morphology Reproductive morphology Flowers Androecium

Lepidagathis has two or four fertile stamens, the anterior anthers are always bithecous, the posterior, when present, can be mono- or bithecous or reduced to staminodia. Bentham (1876) used the number of thecae of the anthers to distinguish Lophostachys from Lepidagathis. All species described under Lophostachys presented monothecous posterior anthers, but among the species described under Lepidagathis there are also some with this character, as noted by Burkill & Clarke (1899) in African species; these authors used it to distinguish two groups in Lepidagathis. The complete reduction of the ventral anthers was found in one species from Madagascar (Lepidagathis grandidieri Benoist) and one from Mexico (L. uxpanapensis), where the filaments are still present as staminodia, and some species with decussate flowers. In bithecous anthers the thecae may be the same size or not, and they may be parallel or divergent.

Morphology Reproductive morphology Flowers Calyx

In Lepidagathis calyces can be very conspicuous, large and colourful, probably helping to attract pollinators, mainly in species described under Lophostachys. The zygomorphic calyx is formed by five unequal sepals, the lateral ones narrower, and very often shorter than the others. The posterior or upper sepal is wider and is generally acrodromous or parallelodromous in the Neotropical species. The two anterior sepals are generally fused to each other to an extent greater than with the lateral sepals and each one can be equal or dimidiate forming a structure (segment) that seems to be a single sepal. Zygomorphic calyces seem to have evolved independently in different groups, since they are present in many unrelated genera. The degree of anterior sepal fusion was one of the features used to distinguish Lophostachys from Lepidagathis (Nees 1847a, b; Bentham 1876) and Lepidagathis from Teliostachya (Bremekamp 1960). Neotropical secundiflorous species always have dimidiate dorsal sepals which are basally fused for at least 1/3 of their length. The Mexican species Lepidagathis chiapensis (Acosta) Kameyama and L. uxpanapensis (Acosta) Kameyama present these sepals almost completely fused. The lateral sepals are much narrower and shorter than the others, and generally linear. In all secundiflorous Neotropical species and in many Paleotropical species the lateral sepals are internal to the ventral and dorsal sepals being overlapped by them, as in Barleria (Balkwill & Balkwill 1997).

Morphology Reproductive morphology Flowers Corolla

The corolla is always bilabiate. The upper lip is entire or shallowly bilobed, and the lower lip is trilobate. Size, shape and colour of corollas are evidently related to pollination. Most of the species have relatively small corollas, between 4 – 20 mm long, with a distinct tube and throat area, the lower lip spreading, white, lilac or pinkish with purple, purplish-red or yellow markings; they are probably pollinated by small or medium-sized insects. Many Neotropical, some Malagasy, and a few African and Asian species have larger corollas, between 2.4 – 6 cm long, generally red, purple-red or white. In Old World species, which are probably pollinated by butterflies, the corolla tube is long, straight and narrow. In Neotropical species, pollinated by hummingbirds, it is wide and curved. The showy corollas are always associated with showy, usually coloured, calyces. All corollas of the secundiflorous species that have been examined have inside the tube, around the base of the style, a ring of long, straight hairs that interweave with a similar ring present at the base of the style. These hairs probably have a protective function.

Morphology Reproductive morphology Flowers Gynoecium

The gynoecium is very uniform among Lepidagathis species. Each locule of the ovary has two ovules; the stigma is subcapitate and shallowly bilobed. At the base, the nectariferous disk is cupulate and covers one quarter to almost half of the ovary. At the base of the style there is a ring of long, straight hairs.

Morphology Reproductive morphology Flowers Pollen

The study of pollen grains of ten species of Lepidagathis (Cruz-Barros et al., pers. comm.) and comparison with literature (Raj 1961; Huang 1972; Rowbik & Moreno 1991; Daniel 1998; Scotland & Vollesen 2000) showed that, except for variation in size and shape from subprolate to prolate, pollen grains in Lepidagathis are very uniform. The pollen is 3-colporate, reticulate, heterobrochate, the lumina are verrucate, pilate or baculate and the lumina adjacent to the colpi, at the poles and the centre of mesolcopi are smaller.

Morphology Reproductive morphology Fruits

As in other species of subtribe Barlerineae, the capsule outline is oblong, elliptic to ovate, apex acute to acuminate, subquadrangular, with relatively thin walls and thick septum, mostly with four seeds, sometimes two. In Lepidagathis. cristata the capsule is indehiscent, the walls are membranaceous, when moist the walls soften and eventually rupture, releasing the seeds.

Morphology Reproductive morphology Inflorescences

Lepidagathis sensu lato has simple (thyrse or spike) or compound indeterminate inflorescences (polytelic), with three basic types of unit, according to Weberling (1989): (a) thyrse, with dichasia of up to 5 flowers as partial fluorescences, as in Lepidagathis alopecuroides (Vahl.) R. Br. ex Griseb. and some other species described under Teliostachya; (b) spikes with decussate flowers, as in Lepidagathis riedeliana Nees and a few other Neotropical and African species; (c) secundiflorous spikes with two rows of sterile bracts and two rows of fertile bracts; the bracts, except the basal, are alternate. This type is present in most species of Lepidagathis.

Morphology Reproductive morphology Seeds

The seeds are lenticular and have hygroscopic trichomes that expand when moist; this type of trichome has evolved independently in unrelated groups of Acanthaceae (Scotland et al. 1995; Manktelow et al. 2001; McDade et al. 2005).

Flora Zambesiaca Acanthaceae (part 2) by Iain Darbyshire, Kaj Vollesen and Ensermu Kelbessa

Morphology General Habit

Perennial herbs and subshrubs.

Morphology Stem

Stems 4-angular to subterete.

Morphology Leaves

Leaves evergreen or deciduous, opposite-decussate, sessile or base decurrent into petiole, blade often with minute sunken glands on lower surface; cystoliths numerous, ± conspicuous.

Morphology Reproductive morphology Inflorescences

Inflorescences of unilateral (scorpioid) fasciculate to spiciform cymes, axillary and/or terminal, often compounded into a dense synflorescence, rarely a dichasial thyrse or flowers solitary; bract pairs equal to dimorphic, free, sterile bracts in unilateral cymes typically imbricate and subtending flowers, fertile bracts and bracteoles usually adpressed to calyx; bracteoles paired, (sub)equal, free.

Morphology Reproductive morphology Flowers Calyx

Calyx divided almost to base, unequally 5-lobed, posterior lobe broader than remaining lobes, anterior pair sometimes partially fused, lateral (inner) pair linear-lanceolate.

Morphology Reproductive morphology Flowers Corolla

Corolla bilabiate; tube cylindrical in lower portion, throat campanulate, base of throat ± densely hairy within; upper lip hooded, straight or arcuate, apex shortly bilobed or shallowly emarginate; lower lip with apex 3-lobed, palate upraised with a central furrow.

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 4, didynamous, filaments arising from near base of corolla throat; anterior pair of stamens longer, bithecous, thecae at an equal height or offset; posterior pair shorter, monothecous or bithecous.

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary bilocular, 1 or 2 ovules per locule; style filiform; stigma capitate-bilobed or one lobe expanded and spoon-shaped.

Morphology Reproductive morphology Fruits

Capsule compressed, 2-seeded, face then ovate, or 4-seeded, face then oblong-elliptic, sometimes with a short sterile apical beak, placental base inelastic.

Morphology Reproductive morphology Seeds

Seeds held on retinacula, discoid or flattened-triangular, clothed in hygroscopic hairs.

Distribution

A genus of around 100 species with a tropical and subtropical distribution.