Stenostephanus (Acanthaceae) in Peru

An account of the hill forest genus Stenostephanus Nees in Peru is presented. The salient characteristics and distribution of the genus are outlined to provide a wider context for the Peruvian species. Five new species, S. antiquorum J.R.I.Wood, S. atrocalyx J.R.I.Wood, S. cuscoensis J.R.I.Wood, S. densiflorus J.R.I.Wood and S. wasshausenii J.R.I.Wood are described as well as two varieties, var. angustissimus J.R.I.Wood and var. hirtiflorus J.R.I.Wood of S. longistamineus (Ruiz & Pav.) V.M.Baum. A key to all species occurring in Peru is provided together with diagnostic summaries of their salient characteristics and maps of their distribution. The new taxa are illustrated with line drawings and their conservation status is assessed.

Stenostephanus Nees is an entirely neotropical genus of around 80 species. It is distributed along mountains from south central Mexico through Central America and then along the Andes from Venezuela south to the Santa Cruz region in central Bolivia. A single species, S. lobeliiformis Nees occurs in the Atlantic Forest of southeastern Brazil. The greatest diversity is found in Colombia from where 29 species are known (Wood 2009(Wood , 2016. There are accounts of the genus in Bolivia (Wasshausen 1999a;Wasshausen & Wood 2004), in Ecuador (Wasshausen 2013) and in Colombia (Wood 1988(Wood , 2009 but no account of the genus has ever been published for Peru. This paper aims to rectify this omission.
Stenostephanus species are herbs or weak subshrubs with decumbent, ascending or erect stems up to about 3 m in height. Cystoliths are present, particularly on the leaves but sometimes also on other vegetative parts. Stems are often swollen at the nodes. Leaves are entire to undulate, usually equal to slightly unequal in each pair but strongly anisophyllous plants are apparently unknown. The inflorescence is commonly a terminal thyrse but small cymes or thyrses may arise in the upper leaf axils. Prominent bracts may be present at the base of the thyrse but diminish in size upwards at each branching point. The whole inflorescence may be glabrous or glandular-hairy, the glandular hairs often developing as the inflorescence matures. The calyx is divided to near the base into five equal, usually narrowly lanceolate lobes, these somewhat accrescent in fruit. The corolla may be tubular, ±suburceolate with four short lobes, or more or less 2-lipped with a simple upper lip and a 3-lobed, often spreading lower lip. In colour, the corolla may be blue, yellow, red, purple, pink or bicoloured. The androecium consists of two, usually exserted stamens, inserted above the basal part of the corolla tube, each stamen with a monothecous anther. The pollen is of a characteristic shape resembling an aeroplane wheel. The gynoecium consists of a narrowly oblong ovary and single style with a very small stigma. The fruit is an oblong 4-seeded, stipitate capsule, the seeds discoid or lenticular, often tuberculate.
The corolla of Stenostephanus is highly variable and variation in its form was the main justification for several segregate genera previously recognised but now subsumed into Stenostephanus. Four corolla types can be discerned in Peruvian species. In S. sprucei (Lindau) Wassh. & J. R.I.Wood, previously placed in Cylindrosolenium Lindau, the three lower corolla lobes are relatively long, linear-filiform, flexuose and resembling the upper lip so the corolla appears to be deeply 4-lobed. S. davidsonii Wassh. and S. macrolobus (Lindau) J.R.I. Wood have strongly 2-lipped corollas but with the lower lip shallowly lobed. Previously they would have been placed in Habracanthus Nees. It is probable that the species treated below as Stenostephanus sp. A also belongs to this group but in the absence of corollas it is impossible to be sure. Weakly 2-lipped are the corollas of S. wallnoeferi Wassh. and S. longistamineus (Ruiz & Pav.) V.M.Baum. These have a bent or falcate corolla tube which is narrowly obovoid in bud. S. longistamineus and its allies also have a rather distinct calyx with short, essentially lanceolate lobes, broad at the base but abruptly narrowed to a filiform apex. The remaining species from Peru belong to a group with a tubular corolla with very short lobes, which were or would have been included in the genus Hansteinia Oerst.
Stenostephanus is a characteristic cloud forest species with a few species occurring in lower altitude rain forest but, apart from S. longistamineus, always on or near mountainous regions. Most species are very local endemics, often known from a single locality or with a very restricted range. Many appear to flower irregularly, perhaps in response to particular climatic conditions. One Mexican species is confirmed to be plietesial (Daniel 2006) but it is quite probable that other species are also plietesial. Species with a tubular red flower (the majority of species in Peru) are presumably hummingbird-pollinated but very little reliable information is known about the pollination of these plants. Species with strongly 2-lipped corollas tend to occur at higher altitudes (1500 -2500 m) than those with a subcylindical corolla.
In morphology, pollen and ecology, Stenostephanus is very similar to the African genus, Brachystephanus Nees and it is difficult to see how the two genera can be consistently distinguished. Champluvier & Darbyshire (2009) compared the two genera in some detail but decided that no attempt to unite them should be made before further molecular studies were made. Stenostephanus is the older name so there is no threat to the nomenclatural stability of the neotropical species.
This paper is essentially based on the study of dried specimens from four herbaria: the Field Museum (F), the Royal Botanic Gardens at Kew (K), Missouri Botanical Garden (MO) and the Smithsonian Institution in Washington (US). Reference has been made to relevant publications, which are cited in the list of references, and observations have been informed by the author's knowledge of the genus in the field, albeit outside Peru. Full descriptions are provided of the five new species and of Stephanus longistamineus, the latter because of the description of two new infraspecific taxa. Diagnostic notes are provided for other recognised species. Maps have been constructed based on the coordinates provided on recent collection labels augmented by inferred coordinates from locations provided by earlier collectors. Species are arranged alphabetically in the following account.
This paper recognises 12 species from Peru, of which are seven are endemic. Five are described as new but there are probably other undescribed species as some specimens cannot be readily assigned to species. This number is similar to that of Ecuador (eight species) and Bolivia (currently 11, but two more in preparation for publication), but much less than that of Colombia (29).
Species occurring in Peru can be distinguished by the following key, but this will only work well with plants that have buds and open corollas.
http://www.ipni.org/urn:lsid:ipni.org:names:60479358-2 Subshrub/woody herb to 1.5 m; stems somewhat sulcate, pubescent in the depressions, glabrescent when old and woody parts glabrous. Leaves petiolate; petioles 0.5 -4 cm, crisped pubescent; lamina oblong-elliptic to obovate, shortly acuminate, base attenuate and somewhat decurrent onto the petiole; both surfaces very thinly to rather densely pubescent, with abundant short cystoliths, abaxially paler and sometimes the veins with denser pubescence; veins 10 -11 pairs. Inflorescence of very lax, few-flowered axillary racemes, arising from the upper leaf axils, often reduced to a few flowers; rhachis 7 -16 cm, densely hirsute; bracts at base of raceme resembling small leaves; at branching points resembling bracteoles; bracteoles linear, minute, c. 1.5 mm long, crisped pubescent; peduncles 5 -15 mm, simple or forked, crisped pubescent; secondary peduncles shorter; pedicels 1 -2 mm; calyx with rounded base c. 1 mm long, 5-lobed, the lobes linear-attenuate 6 -9 (-13) mm long, somewhat accrescent in fruit, very sparsely and shortly hirsute; corolla 2 -3.5 cm, red, subcylindrical, the basal part narrow up to 9 mm long, 1 -2 mm wide, then slightly, but abruptly widened to 3 -4 mm, the tube nearly glabrous but the apical portion with a few scattered hairs, obscurely 2-lipped, the upper lip lanceolate, c. 5 mm long, the lower lip shorter, with short oblong lobes c. 2 mm long; filaments glabrous, anthers exserted to 12 mm, 4 mm long; style 3.1 mm long, glabrous, persistent; stigma globose, ovary hirsute. Capsule 15 × 2.5 mm, clavate, hirsute; 4-seeded; seeds lenticular, 2.25 × 1.5 mm, reticulate. Fig. 1A -M. RECOGNITION. Resembles Stenostephanus crenulatus (Britton ex Rusby) Wassh. in the shape and colour of the corolla and appearance of the inflorescence but differs in the hirsute (not glabrous) ovary and capsule, shortly pubescent (not glabrous) corolla and especially in the shape of the calyx whose lobes are linearfiliform 6 -11 mm in length, not deltoid, 2 -3 mm long. HABITAT & DISTRIBUTION. Humid montane forest usually between 2100 -2800 m in the Peruvian Andes. With an area of occupancy of 48,000 km 2 and an extent of occurrence of 3178.183 km 2 , based on Geocat, this species should be provisionally classified as Endangered (EN) following IUCN guidelines. Some sites lie within the Area de Conservación Regional Choquequirao but Andean forest is very vulnerable to clearance and it is not clear how secure the conservation area is. EPONYMY. This species is named "antiquorum" because it is chiefly found around Macchu Pichu, the most famous remains of ancient civilisation in Peru. Stenostephanus atrocalyx J. R.I.Wood, sp. nov. Type: Peru, Cusco, Quispicanchis, along trail 25 km SW of Quincemil, 1340, D. C. Wasshausen & F. Encarnación 744 (holotype US2957324, isotype K).

RECOGNITION. Resembles Stenostephanus lobeliiformis
Nees and S. lyman-smithii Wassh. in the elongate racemose inflorescence and tubular corolla with short lips but differs from both these species in the hirsute leaves (not glabrous to thinly pubescent on the veins), the larger corolla, 2.1 -2.7 cm long (not 1.5 -2 cm long), densely spreading (not finely appressed) pubescence on the exterior of the corolla and in the more finely filiform-attenuate calyx lobes. With an area of occupancy of 12,000 km 2 and an extent of occurrence of 865.479 km 2 , based on Geocat, this species should be provisionally classified as Endangered (EN) according to IUCN guidelines. It is only known from four collections, two made more than 50 years ago and its forest habitat is vulnerable to clearance. Further studies are needed to confirm the classification but, unless further populations are found, a classification of CR (Critically Endangered) may prove to be more correct. EPONYMY. This species is named "cuscoensis" after the Cusco region to which it is endemic.
NOMENCLATURE & TYPIFICATION. The epithet longistaminea (with "e") was inexplicitly changed to longistaminus (without "e") by Baum (1982) when making the combination in Stenostephanus. Most recent publications have followed this spelling but the original, as used by Ruiz & Pavon, should be used. This species is sometimes filed, as in Madrid, under the name Odontonema longistamineum (Ruiz & Pav.) Kuntze, but this appears to be a nomen nudum as it was never published. The photograph of the Berlin specimen of Stenostephanus thyrsoides at the Field Museum (FOBN008836) does not appear to be an image of the type as it is labelled as Weberbauer 6798. It is possible that the holotype was never at Berlin although there is nothing to indicate this in the protologue.

NOTE.
Stenostephanus longistamineus is an exceptionally widespread species, occurring in three countries (Map 5), and is also exceptionally variable. Variation is most marked in the form of the inflorescence (subspicate to a lax thyrse), in the size of the inflorescence (short and much exceeded by the subtending leaves, to elongate and much exceeding the subtending leaves), inflorescence indumentum (glabrous to densely hirsute) and to a lesser extent corolla size and indumentum. I originally thought several distinct species were involved but examina-tion of a large number of specimens revealed overlapping characters and overlapping distribution ranges (Map 5). I have consequently recognised three varieties which are readily recognised although there exist specimens which are difficult to assign. I suspect S. wallnoeferi may also prove to be only a variety of S. longostamineus but as the corolla size and distribution range (Map 5) lie somewhat outside that of S. longistamineus, I have maintained it as a distinct species. I recognise the following three varieties: Map 5