Psednotrichia perennis (Asteraceae, Senecioneae): A new species from the Huila plateau, Angola

The genus Psednotrichia (Asteraceae–Senecioneae) is endemic to Angola and currently consists of two annual species, P. xyridopsis (O. Hoffm.) Anderb. & P. O. Karis, and P. newtonii (O. Hoffm.) Anderb. & P. O. Karis. A perennial member of the genus was collected on a recent field trip to Angola, and is here described as P. perennis N. G. Bergh & B. Nord., sp. nov. A key to the three species is provided. © 2010 SAAB. Published by Elsevier B.V. All rights reserved.


Introduction
Of the approximately 370 species of Asteraceae recorded for Angola (Figueiredo and Smith, 2008), a small but significant portionviz. about 64 species (or 17 %)belong to the tribe Senecioneae. Most of these are in the genus Senecio L., with the remaining genera represented by just a few species each. Psednotrichia Hiern. is one of these small genera and until now consisted of only two species, both of which are annual and endemic to Angola. They were first described (Hoffmann, 1896) as members of the genus Oligothrix DC. but were later distinguished as a separate genus, Xyridopsis B. Nord. (Nordenstam, 1978). This left Oligothrix as a monotypic genus confined to the Cape Province of South Africa. Apart from in its geographical distribution Psednotrichia differs from Oligothrix in habit, leaf-shape and floral characters, such as the discoid capitula and style branches with penicillate apices.
Although both Xyridopsis species were sunk into Emilia by Jeffrey (1986), this was later reversed by Anderberg and Karis (1995). In the same publication, Anderberg and Karis examined the floral anatomy of the little-known species Psednotrichia tenella Hiern., described in 1898 (Hiern, 1898)  The affinities of Psednotrichia need further inquiry. Although Jeffrey (1986Jeffrey ( , 1992 included the genus in Emilia, its separation from Emilia was upheld by Bremer (1994, as Xyridopsis) and (as Psednotrichia) by Anderberg and Karis (1995) and Nordenstam (2007). Jeffrey's (1986) inclusion of Xyridopsis in Emilia was based on his hypothesis that all African taxa with "emilioid" characters (ecalyculate involucres and a unique base chromosome number of n = 5) were best placed in one genus, despite the fact that the chromosome number of Xyridopsis/Psednotrichia has never been investigated. Anderberg and Karis (1995) justified the separation of Xyridopsis from Emilia on the grounds that the former shares characters such as mucilaginous cypsela hairs, scapose peduncles, ecalyculate involucres and resiniferous corolla with other genera in the Senecioneae. In addition, these authors considered that Emilia is large and heterogeneous, and anticipated future splitting of the genus. The circumscription of Emilia, Senecio and other genera awaits further analysis. Due to political conflict, botanical research has been all but suspended in Angola for several decades. With the resumption of peace and the rebuilding of the country, there is scope for continuance of the botanical tradition in the flora of Angola. The following new species was collected during a botanical excursion to southern Angola at the start of 2009, in the high-altitude grassland of the Huila plateau ( Fig. 1). Despite its anomalous perennial life-history it is evidently a species of Psednotrichia on account of the linear leaves, ecalyculate, discoid capitulum with partially connate involucre (Figs. 1 and 2) and the characteristic features of the florets (truncate style branches with a central penicillate tuft, the swollen stamen filament collar, mucilaginous cypsela hairs and flexuous, barbellate pappus bristles; Fig. 2). The new species may be closest to P. xyridopsis as they both have contracted stems resulting in basal, sub-rosulate leaves, while in P. newtonii the leaves are distributed along a more elongate stem. The perennial habit is an important addition to the morphological range in the genus.

Species sampling and description
Plant, habitat and location details were recorded and plants were photographed in situ. Vouchers were deposited at the Compton Herbarium, Cape Town (NBG), Pretoria Herbarium (PRE), Swedish Museum of Natural History, Stockholm (S) and at Lubango Herbarium in Angola (LUBA). Morphological characters were examined under stereo-and dissection microscopes and camera lucida attachments were used to create detailed drawings.

Flowering time
Observed in flower in January.

Distribution, ecology and conservation status
The new species is so far known only from a restricted area of grassland on sandstone-derived quartzitic sand, near the edge of a dry rivulet on the high-altitude plateau of Huila Province, Angola (Figs. 1a and 3). This type of habitat is very restricted in Angola, being confined to the Huila plateau and a small patch north-east of Lobito. Nevertheless, the afro-temperate plateaux with altitudes above 2000 m are among the most species-rich areas in Southern Angola. The species may be classified as Vulnerable according to IUCN criteria but has not been formally assessed.

Diagnosis and relationships
Psednotrichia newtonii (O. Hoffm.) Anderb. & P. O. Karis, is annual and poorly known, but has a different habit with more leafy and branching stems, and is recorded as growing on the margins of the Pallanca River, in the vicinity of Lubango. P. perennis is more similar to P. xyridopsis in leaf arrangement and floral details such as the slight asymmetry of the florets, median resin duct in the corolla lobes, the style branch morphology with a small central tuft to the penicillate apex, the much swollen filament collars and the short, rounded-clavate duplex cypselar hairs which become mucilaginous when soaked. In addition, P. xyridopsis and the new taxon may be sympatric, both being known only from the Huila plateau near the town of Humpata, although no individuals of P. xyridopsis were observed at the time of collection of P. perennis.
A possibility we considered is that the new taxon is conspecific with P. xyridopsis, which would require that the interpretation that the latter is an annual is incorrect. This would be possible especially if all material happened to have been collected off very young plants. It is not always possible to distinguish the annual life-history from herbarium specimens, but several collections of P. xyridopsis are annotated as 'annual' by the collectors who saw the live plants in the field (e.g. B. Fritzsche 137). The new species also differs from P. xyridopsis (Fig. 4) in several other features: it has a generally Fig. 3. Map of Angola and its provinces with the known distribution of Psednotrichia perennis indicated by a black filled circle. larger and more robust habit with relatively longer and stouter peduncles as well as larger capitula, and copious silky wool between the leaf bases. We compared several specimens of P. xyridopsis (F. M. J. Welwitsch 3992; B. Fritzsche 137; L. E. Kers s.n.) with the new taxon to confirm that the former does indeed appear to be annual and differs from the latter in several characters. P. xyridopsis is a shorter, more gracile plant with a thinner base and slender annual roots, and the tomentum between the leaf bases is lax and sparse or absent. The coarser habit of the perennial taxon is also manifest in the length and thickness of the leaves (30-120 × 0.7-1.5 mm, as compared to 20-40 × 0.5-0.7 mm in P. xyridopsis) and peduncles (150-350 × 0.7-1.0 mm, as compared to 100-200 × 0.5-0.7 mm in P. xyridopsis). Capitula are larger in the perennial taxon (10-13 mm as opposed to 7-10 mm diam. in P. xyridopsis) with generally larger involucral bracts (4.5-7.0 × 1.0-3.0 mm as compared with P. xyridopsis where they are 4.0-5.0 × 1.0-2.0 mm). The peduncles are also less distinctly swollen below the capitulum in P. xyridopsis, and the pappus bristles somewhat shorter, only 0.5-1.0 mm as opposed to 1.5-2.0 mm in length in the perennial species.
All three species occur in and around the Huila plateau in Angola and thus share a fairly narrow distribution range. There appears to be some separation of flowering time between