Introduction

Stenostephanus Nees is a neotropical genus of about 90 species characterised by its monothecous anthers and the distinctive lenticular pollen with a pronounced marginal girdle fancifully resembling an aeroplane wheel. Its range extends from southern Mexico through Central America and then along the Andes from Venezuela to central Bolivia with a single species in the Brazilian Atlantic Forest (Wood 2019b). It is mainly a genus of montane cloud forest from the Andean foothills around 500 m to about 3000 m but a few species occur in rainforest east of the Andes. It reaches its greatest diversity in the Andes of Colombia followed by Peru, Bolivia and Ecuador (Wasshausen 2013; Wood 2016, 2019a, 2019b).

In Peru, Stenostephanus is distributed through the Andean Departments with relatively high rainfall, the highest number of species (7) being in Huánuco, but it is almost completely absent from the departments with an arid climate adjoining the Pacific Ocean. Wood (2019b) highlighted the restricted range of many Stenostephanus species recognising six species endemic to Peru: S. antiquorum J.R.I.Wood, S. atrocalyx J.R.I.Wood, S. densiflorus J.R.I.Wood, S. macrolobus (Lindau) J.R.I.Wood, S. wallnoeferi Wassh. and S. wasshausenii J.R.I.Wood.

Following examination of herbarium collections and associated photographs, a new species of Stenostephanus is recognised from Junín. This species is described below as S. brevistamineus R.Villanueva & J.R.I.Wood. Additionally, herbarium material of another undescribed species from Loreto was found in the Kew herbarium and this too is described below in Stenostephanus as S. borarum J.R.I.Wood & R.Villanueva. Previously this would have been placed in Kalbreyeriella Lindau or Razisea Oerst. but it is now accepted that these genera, like other neotropical species of the Isoglossinae with monothecous anthers, should be treated as belonging to Stenostephanus as molecular studies give no support for the recognition of either of these two genera (Kiel et al. 2006; McDade et al. 2019; Manzitto-Tripp et al. 2022). The transfer of the only previously recognised Peruvian species of Razisea to Stenostephanus as S. ericae (Mildbr. ex Wassh.) J.R.I.Wood & R.Villanueva and the recent transfer of the only Peruvian species of Kalbreyeriella Lindau to Stenostephanus as S. rostellatus (Lindau) T.F.Daniel, McDade & Kiel (Manzitto-Tripp et al. 2022: 144) brings the total number of Stenostephanus species in Peru to 16 of which eight are endemic to the country.

Materials & Methods

Herbarium collections from HOXA, K, MO and USM and photographs were examined for morphological details. Maps were elaborated using the Geographical Mapping program ArcGis Pro 2.8.4 and the elevation data from the WorldClim version 2.1 (Fick & Hijmans 2017). The conservation status was assessed following IUCN Guidelines (2019) based on estimates of Extent of Occurrence (EOO) calculated using the GeoCat Geospatial Conservation Assessment Tool (http://geocat.kew.org) (Bachman et al. 2011).

Taxonomic Treatment

Stenostephanus brevistamineus R.Villanueva & J.R.I.Wood, sp. nov. Type: Peru, Junín, Prov. Satipo, Distr. Rio Tambo, Comunidad Nativa Pichiquia, Parque Nacional Otishi, 11°22'28"S 73°59'28"W, 2060 m, 11 July 2013, L. Valenzuela, J. Flores, G. Shareva, Z. Ganz, J. Carhuacosme & V. Flores 24907 (holotype HOXA-065350!; isotypes MO!, USM!).

http://www.ipni.org/urn:lsid:ipni.org:names:77304117-1

Perennial subshrub to c. 1 m tall; stem erect, simple below, much-branched above, quadrangular, glabrous, the nodes swollen. Leaves slightly unequal in each pair, petiolate, glabrous; lamina membranaceous, 3.8 – 10.5 × 0.8 – 3.5 cm, oblong-elliptic, apex acuminate, base acute, margin entire, slightly undulate, venation camptodromous, lateral veins 6 – 8 pairs, adaxially, green, with numerous small cystoliths and impressed veins, abaxially shiny, veins prominent, reticulate; petiole 0.2 – 1.3 cm long. Inflorescence a pedunculate, ovoid, lavender terminal thyrse, 3 – 8 × 5 cm; peduncle 1 – 6 cm long, pubescent; rachis densely glandular-pubescent, the flowers arranged in opposite-decussate 3-flowered dichasia, the central flower subsessile, the laterals pedicellate with terete, pubescent pedicels to 2 mm in length; bracts at branching points 2 – 2.5 mm long, deltoid, acute, glabrous or nearly so; bracteoles 1.5 – 3 mm long, equal, linear, puberulent; calyx subequally 5-lobed to near the base, lobes linear, acuminate often with recurved apex, 7 – 8.5 × 0.5 mm, shortly puberulent, light green; corolla obscurely 2-lipped, subequally 4-lobed, 7 – 7.5 mm long, lavender; tube 4 – 6 mm long, 1 – 1.5 mm diam, ±equalling lobes, glabrous; lobes 4.5 – 5 × 1 mm, oblong, rounded, equal, glabrous; stamens 2, filaments glabrous, 3 mm long; anthers 2 mm long, muticous, glabrous, held at corolla mouth; style c. 6 mm, glabrous; stigma head subglobose, flattened; ovary pubescent. Capsule 10 – 11 × 2.5 mm, clavate, densely pubescent; seeds 4, 1 × 1 mm, elliptic, yellowish-brown, muricate. Figs 1 – 3.

Fig. 1
figure 1

Stenostephanus brevistamineus A habit; B adaxial surface of lamina showing cystoliths; C calyx; D corolla opened out showing lobing, stamens, style and stigma; E fruiting inflorescence branch showing capsules; F seed. From Valenzuela 24907 and photos. drawn by rosemary wise.

Full size image
Fig. 2
figure 2

Stenostephanus brevistamineus. Thyrse with lavender flowers, type. photo: l. valenzuela.

Full size image
Fig. 3
figure 3

Stenostephanus brevistamineus. Detail of part of inflorescence of holotype, showing calyx, corolla, theca and stigma

Full size image

recognition. Stenostephanus brevistamineus resembles S. macrolobus in the filiform calyx lobes and subequally 4-lobed corolla but the whole inflorescence is lavender in colour (Fig. 2), the calyx lobes are almost equal in length to the corolla (Fig. 3) (in S. macrolobus, much shorter than the corolla), the corolla is shorter 7 – 7.5 mm long (vs 14 mm long) and anthers are held at the corolla mouth (vs exserted). The subequal corolla lobes (Fig. 3) suggest an affinity with S. tenellus Wassh. & J.R.I.Wood and S. sprucei (Lindau) Wassh., but the open pyramidal thyrse distinguishes the new species from these two whose inflorescence is spicate in form and whose anthers are strongly exserted.

habitat & distribution. Stenostephanus brevistamineus is a perennial herb endemic to the Otishi National Park in the Rio Tambo district (Junín, Peru) at 2060 m. It grows in undisturbed montane sclerophyllous forests with humus-enriched soils. Map 1.

Map 1
figure 4

Map of Peru showing distribution of Stenostephanus brevistamineus () and S. borarum ().

Full size image

conservation status. Stenostephanus brevistamineus is only known from its type locality corresponding to the Otishi National Park, where very few explorations have been carried out. Currently, the surrounding areas are being affected by habitat destruction and exploitation of natural resources, but this has not yet impacted on the park itself (INRENA 2003). Therefore, we assign this species to the category Data Deficient (DD) according to IUCN (2019). However, this category could change in the future if more information becomes available.

phenology. Stenostephanus brevistamineus was observed with flowers and fruits in July.

etymology. The specific epithet refers to its short stamens, the anthers only reaching the corolla mouth.

taxonomic notes. Species of Stenostephanus are mostly distinguished by the shape of the inflorescence and the colour and shape of the corolla. The new species is distinguished in part by the pyramidal thyrse which is almost entirely lavender in colour (Fig. 2). At one level, the corolla is unremarkable in that it resembles many species in having four subequal lobes and is obscurely 2-lipped. However, the lobes are long relative to the basal tube, but not flexuose or recurved, and the anthers are held at the corolla mouth, not exserted. Also unusual are the relative lengths of the calyx and the corolla. These are similar in length (Fig. 3) whereas in most species the corolla much exceeds the calyx. S. brevistamineus is probably most closely related to S. macrolobus and is somewhat similar in inflorescence structure but is readily distinguished by its distinctive colour, subequally 4-lobed corolla with stamens included in the corolla mouth and long calyx relative to the corolla. It might be interpreted as being similar to S. sprucei (Lindau) Wassh. but this and similar species like S. tenellus Wassh. & J.R.I.Wood, have a spike-like inflorescence with flowers in fascicles along the rhachis besides other distinguishing characters. These differences are set out in more detail in Table 1.

Table 1. Morphological comparison of Neotropical species of Stenostephanus similar to Stenostephanus brevistamineus.
Full size table

Molecular studies (Kiel et al. 2006) have suggested that Razisea and other American genera of the Isoglossinae Lindau should be included within a more broadly defined Stenostephanus but the necessary transfers were not made until a recent paper by McDade et al. (2019). This left the only Peruvian representative of the genus unplaced in Stenostephanus so we make the appropriate combination below:

Stenostephanus ericae (Mildbr. ex Wassh.) J.R.I.Wood & R.Villanueva, comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77304118-1

Razisea ericae Mildbr. ex Wassh., Novon 7 (2): 88 (Wasshausen 1997). Type: Ecuador, Napo, vicinity of Hacienda Dos Rios, Erica Henrichs 309 (holotype G).

Wasshausen (1997) cited eight records from Peru, four from Amazonas and four from Loreto. There are several more records in Tropicos (https://www.tropicos.org/) but hardly any more information about its habitat. It appears to be a species of humid forest growing between 130 and 1700 m, but definitely more common at lower altitudes (Fig. 4).

Fig. 4
figure 5

Stenostephanus ericae. Photograph of I. Huamantupa et al. 15882 from Cerros Kampankis, Condorcanqui, Distr. Santiago, Dept. Amazonas. photo: © isau huamantupa.

Full size image
Fig. 5
figure 6

Stenostephanus borarum. A habit; B abaxial surface of young lamina showing cystoliths; C flower showing, bract, bracteole and calyx; D bract; E bracteole; F calyx; G corolla opened out to show filaments, anthers ovary, style and stigma. From Barrier 912. drawn by rosemary wise.

Full size image

During the examination of unidentified Acanthaceae in the Kew herbarium, two sheets of an unidentified species of Stenostephanus were found corresponding to a plant that would previously have been placed in Razisea or Kalbreyeriella. This species is described below:

Stenostephanus borarum J.R.I.Wood & R.Villanueva, sp. nov. Type: Peru, Loreto, Prov. Maynas, Rio Zumun (see note below) affluent du Rio Yahaus-Yaci, affluent de Amazon at Pebas, Commune de Colonoa, terretoire des indiens, Bora Primary Forest, by river, 1 June 1978, S. Barrier 912 (holotype K, specimen with many corollas, isotypes K!, P!) (Fig. 5).

http://www.ipni.org/urn:lsid:ipni.org:names:77304119-1

Perennial herb; stems glabrous, sulcate. Leaves petiolate, slightly unequal in each pair; lamina 4.5 – 10 × 3 – 4.5 cm, elliptic to subrhomboid, apex shortly acuminate, base broadly to narrowly cuneate, slightly oblique, margin entire, veins 10 – 12 pairs, both surfaces with prominent cystoliths, adaxially glabrous, abaxially glabrous except for the obscurely strigose veins on young leaves; petioles 1 – 4 cm, glabrous. Inflorescence a spike-like reduced thyrse, mostly terminal on the main stem but also from the uppermost leaf axils, 8 – 11 cm long; rhachis bifariously puberulent, flowerless only in the lowermost 1 – 3 cm; flowers mostly sessile but with lowermost borne on puberulent pedicels 1 – 2 mm long; bracts oblong-lanceolate, glabrous 4 – 6 × 1 – 2 mm; bracteoles 12 – 23 × 2 – 3 mm, linear-lanceolate, acuminate, glabrous, prominently veined; calyx 5-lobed to base, lobes 10 – 15 × 1 – 1.5 mm, two slightly broader than the other three, linear, finely acuminate, glabrous; corolla 2.8 – 3.5 cm long, 5 – 6 mm wide, red, glabrous on the exterior, subcylindrical in bud with an erect subacute apex, weakly curved, slightly widened apically at anthesis, 2-lipped, lower lip appearing entire, ovate-deltoid, 4 – 6 mm long, accrescent at anthesis, upper lip linear-lanceolate, 6 × 2 mm, entire or subentire; stamens exserted 1 – 3 mm, glabrous, filaments c. 25 mm long, glabrous, anthers 2 – 2.5 × 0.5 mm; style 25 – 30 mm long, glabrous, equalling stamens, stigma capitate; ovary glabrous. Capsule not seen.

recognition. This species would previously have been placed in the genus Razisea because of its spicate inflorescence and curved corolla with erect upper lip. It resembles two other species previously placed in Razisea, the relatively widespread Stenostephanus leiorhachis (Lindau) Hammel in McDade et al. (2019: 41) (= Razisea spicata Oerst.) and Stenostephanus ericae from Peru and Ecuador but it is readily distinguished from the former by the shorter corolla 2.8 – 3.5 cm (vs 4.7 – 6 cm) and much longer bracteoles 12 – 23 mm (vs 5 mm) and from the latter by the linear-lanceolate bracts up to 15 mm long (vs 2 – 3 mm long) and the linear calyx lobes 10 – 15 mm long (vs 3 – 4 mm long). The new species also bears a strong resemblance to Stenostephanus rostellatus (= Kalbreyeriella rostellata Lindau) but differs inter alia by the elliptic to subrhomboid (vs oblong-elliptic) leaves, the shorter calyx divided to the base c. 12 mm long (vs 16 – 18 mm long) with lobes 1 – 1.5 mm wide (not up to 3 mm), the smaller corolla to 3.5 cm long (not 4.5 – 5.5 cm), the narrower tube c. 6 mm wide (vs 9 – 12 mm wide), much shorter corolla lips 6 mm long (vs 13 mm) and the barely exserted anthers. Table 2.

Table 2. Morphological comparison between species of Stenostephanus similar to Stenostephanus borarum.
Full size table

habitat & distribution. Only known from the type collection made in Amazonian Peru in primary [rain] forest at an altitude of approximately 100 m. However, there are several apparent errors in the information provided on the collection label. Pebas lies in Mariscal Ramón Castilla Province, the Rio Zuman is probably the Rio Sumón and the plant is most unlikely to be a liana as described on the label. Map 1.

conservation status. Stenostephanus borarum is only known from its type locality in Bora Primary Forest near Pebas in Amazonian Peru. We have no information about the size of the population or of the current state of the forest where it was found or potential threats in the future. Therefore, we have no option but to assign this species to the category Data Deficient (DD) according to (IUCN 2019).

phenology. Stenostephanus borarum was observed with flowers in June.

etymology. The specific epithet refers to the Bora people indigenous community in whose lands the type collection was found.

taxonomic notes. Stenostephanus borarum resembles S. ericae, S. leiorhachis and S. rostellata in habit, leaf shape and the form and colour of the inflorescence but is immediately distinguished by a range of characters as set out in Table 2.