Isoglossa namuliensis I.Darbysh. & T.Harris

Harris, T., Darbyshire, I. & Polhill, R. Kew Bull (2011) 66: 241. https://doi.org/10.1007/s12225-011-9277-9

Morphology General Habit

Weakly decumbent perennial herb, stems to 70 cm long and 15 cm tall in the single specimen seen but probably attaining greater height, rooting at lower nodes

Morphology Stem

Stems quadrangular and furrowed when young, subangular when mature, green with swollen nodes purple, shortly crisped-pubescent when young, hairs mainly retrorse, later glabrescent

Morphology Leaves

Leaves: petiole 18 – 40 mm long, antrorse-pubescent, hairs longest on the upper margins; blade 10 – 12.5 × 3.3 – 4.5 cm, elliptic, base cuneate-attenuate, margin subentire, apex acuminate, principal veins and margin shortly pubescent; lateral veins 6 – 8 pairs

Morphology Reproductive morphology Inflorescences

Inflorescence terminal, a spiciformthyrse, c. 7.5 cm long, each cymule single-flowered, flowers sessile; axis antrorse-pubescent and with scattered patent glandular hairs increasing upwards; bracts 9 – 11.5 × 4.5 – 7 mm, flabellate with a pronounced, outcurved acumen, 4 – 4.5 mm long, margin with 1 – 4 prominent teeth below the acumen, surface green, somewhat paler towards base, eglandular-pubescent, hairs longest on margin and midrib, and with interspersed short glandular hairs; bracteoles 7 – 8.5 × 0.8 – 1.5 mm, linear-lanceolate, pale green with darker midrib

Morphology Reproductive morphology Flowers Calyx

Calyx lobes 6.7 – 8.2 mm long in flower, linear-lanceolate, shortly eglandular-pubescent with interspersed short glandular hairs

Morphology Reproductive morphology Flowers Corolla

Corolla 14.5 – 16.5 mm long, white with maroon markings on palate of lower lip and throat; limb sparsely pubescent outside mainly towards apex of lobes; tube c. 4 mm long, subcampanulate, with a ring of hairs within immediately below insertion point of stamens; upper lip c. 11.5 mm long, lobes 1.2 – 2.3 mm long; lower lip 10 – 12.5 mm long, palate minutely papillose, with raised “herring-bone” venation, lobes 3.5 – 4 mm long, oblong, median lobe wider than lateral pair

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens attached in upper half of corolla tube; filaments free for 4 – 4.5 mm, glabrous; anthers exserted, thecae superposed and separated by c. 1 mm, upper theca 1.6 – 1.8 mm long, parallel or somewhat oblique to the filament, lower theca 1.35 – 1.5 mm long, held ± patent to filament

Morphology Reproductive morphology Flowers Pollen

Pollen gürtelpollen (biporate, circular in polar view and with a marginal girdle)

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary glabrous; style ± 6 mm long, glabrous

Morphology Reproductive morphology Fruits

Capsule and seeds not seen.

Distribution

Mt Namuli, Mozambique, known only from the type.

Ecology

Recorded from a pathside in moist montane Podocarpus-Syzygium forest with the understorey including Cyathea; alt. 1890 m.

Conservation

During the November 2007 expedition to Mt Namuli, evidence of small-scale forest clearance through burning for potato farming was found along the Rio Licungo valley, the single known locality for Isoglossanamuliensis. The combination of a single subpopulation and a projected decline in habitat quality currently qualifies this species as Critically Endangered (CR B1ab(iii) + B2ab(iii)). If, as predicted, this species has a plietesial ecology (see below) it may prove to be more widespread or even locally abundant in the forests of Namuli. However, this unusual ecology, in which the number of mature individuals varies widely year on year, would in any case qualify this species as CR under criterion B1/2 ac(iv).

Note

Only a single flowering spike of this species was found during the November 2007 visit, despite the large extent of suitable habitat on the mountain. Several species of Isoglossa are known to have a plietesial life-cycle, i.e. perennial monocarpy and synchronous periodic flowering of populations (see Darbyshire2009). These include the related I. substrobilina (Tweedie 1965) and I. woodii (van Steenis1978), and a plietesial life-cycle is also inferred for I. milanjiensis from collecting notes on herbarium collections. In such species, it is not uncommon to find occasional plants flowering outside of the “mass flowering” years. It is therefore quite possible that I. namuliensis is a further plietesial species. This, together with the few previous botanical expeditions to Mt Namuli, may help to explain the lack of previous collections of this species. Isoglossanamuliensis falls within a group of closely allied species recorded from eastern Africa (I. substrobilina C. B. Clarke, I. bracteosaMildbr. and I. milanjiensis S. Moore) and in southern Africa (I. woodii C. B. Clarke and allies; see Poriazis & Balkwill2008). Throughout this group the inflorescences are spiciform or paniculate thyrses with sessile flowers subtended by conspicuous bracts, the corollas are small with a conspicuously upraised and “herring-bone” patterned palate to the lower lip, and the anther thecae are superposed and strongly oblique to the filaments. Within this complex, I. namuliensis is both geographically and morphologically closest to I. milanjiensis S. Moore which occurs on Mt Mulanje in S Malawi, Mt Gorongosa in C Mozambique and the Inyanga-Vumba highlands on the Zimbabwe-Mozambique border. It differs in the bracts having 1 – 4 conspicuous slender teeth along each margin (a character which separates it from all other species in this complex), a prominent linear acumen 4 – 4.5 mm long and numerous minute eglandular hairs on the outer surface in addition to the scattered glandular hairs. In I. milanjiensis the bracts subtending each flower (Fig. 2G)1 have an entire or at most minutely and bluntly toothed margin, the acumen is short, 0.5 – 2.5 mm long, or absent and the surface lacks eglandular hairs except along the margin and midrib (glandular hairs varying from absent to dense). In addition, I. namuliensis has longer bracteoles, 7 – 8.5 mm versus 3 – 6.5 mm, and the lobes to the lower lip of the corolla are oblong and 3.5 – 4 mm long, not rounded and 1 – 2.5 mm long. The southern African members of this complex are currently under revision by K. Balkwill and D. Poriazis at the University of Witwatersrand.

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation

Predicted extinction risk: threatened. Confidence: confident

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

Morphology General Habit

Weakly decumbent perennial herb to 15 cm high, stems to 70 cm long, but probably taller, rooting at lower nodes.

Morphology Stem

Stems shortly crisped-pubescent when young, hairs mainly retrorse, later glabrescent.

Morphology Leaves

Leaves elliptic, 10–12.5 × 3.3–4.5 cm, base cuneate-attenuate, apex acuminate, main veins and margin shortly pubescent; lateral veins 6–8 pairs; petiole 18–40 mm long, antrorse-pubescent.

Morphology Reproductive morphology Inflorescences

Inflorescence terminal, spiciform, 7.5 cm long, cymules single-flowered, sessile; axis antrorse-pubescent, with scattered spreading glandular hairs increasing upwards; bracts flabellate, 9–11.5 × 4.5–7 mm, with pronounced outcurved acumen 4–4.5 mm long, margin with 1–5 prominent teeth below acumen, surface pubescent, hairs longest on margin and midrib, with interspersed short glandular hairs; bracteoles linear-lanceolate, 7–8.5 × 0.8–1.5 mm.

Morphology Reproductive morphology Flowers Calyx

Calyx lobes linear-lanceolate, 6.7–8.2 mm long in flower, shortly pubescent with interspersed short glandular hairs.

Morphology Reproductive morphology Flowers Corolla

Corolla 14.5–16.5 mm long, white with maroon markings on palate of lower lip and throat; limb sparsely pubescent externally; tube c.4 mm long, somewhat widened upwards, with a ring of hairs within immediately below attachment point of stamens; upper lip c.11.5 mm long, lobes 1.2–2.3 mm; lower lip 10–12.5 mm long, lobes oblong, 3.5–4 mm, palate upraised and with prominent herring-bone patterning.

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens attached in upper half of corolla tube; filaments free for 4–4.5 mm; anther thecae superposed, upper theca 1.6–1.8 mm long, parallel or somewhat oblique to filament, lower theca 1.35–1.5 mm long, ± patent to filament.

Morphology Reproductive morphology Fruits

Capsule and seeds not seen.

Distribution

Not known elsewhere.

Ecology

Pathside in moist Podocarpus–Syzygium forest; c.1900 m.

Conservation

Conservation notes: Assessed as Critically Endangered under IUCN criterion B in Harris, Darbyshire & Polhill (Kew Bull. 66: 244, 2011).