Reestablishment of Pycreus section Tuberculati ( Cyperaceae )

Pycreus sect. Tuberculati was created by Chermezon to contain a single species with derived nutlets: P. divulsus, a Malagasy endemic. Kukenthal transferred this species to his new section Muricati. However, a detailed study of the nutlet epidermis shows P. divulsus is not closely related to the other species Kukenthal placed in the latter section. In addition P. divulsus subsp. africanus is upgraded to the species level based on its larger, smooth nutlets and African continental range.


INTRODUCTION
The genus Pycreus P.Beauv.consists of around 120, mainly African species, all characterised by their combination of indehiscent spikelets with distichous glumes and laterally compressed pistils with only two style branches.Along with several other genera, Pycreus is nested within the C 4 clade of Cyperus (Muasya et al. 2001(Muasya et al. , 2002)), showing many typical characteristics of this clade, such as an anthela composed of spikes and chlorocyperoid anatomy (Bruhl & Perry 1995, Soros & Bruhl 2000).
Pycreus divulsus (Ridl.)C.B.Clarke is an annual Madagascan endemic differing from the other Pycreus species by its reduced, simply spicate inflorescence comprising a few large spikelets, each sessile in the axil of a large bract and arranged in a single spike.In addition, the internodes of the main axis are elongated (Hooper 1972), (Fig. 1a, b).Inflorescence reductions are quite common in Pycreus and related genera, and can be found in either annual species from seasonal habitats (e.g., P. melanacme Nelmes, P. pauper (Hochst.ex A.Rich.) C.B.Clarke, P. atrorubidus Nees from the Soudano-Zambezian floristic region) or in perennial species with dense fibrous culm bases, living in extreme habitats such as at high altitudes on mountains (e.g.P. gracillimus Chiov.) or frequently burnt vegetation (P.fibrillosus (Kük.)Cherm., P. diloloensis Kük.ex Cherm.).However, the combination of reduction and elongation of the internodes is unique to P. divulsus.
It is not only the inflorescence that makes this plant peculiar among other Pycreus species.The fruits also show special characteristics, which has led to several controversial classifications.At the time of its publication (Ridley 1884), a subgeneric classification for Pycreus was not yet available.Ridley (1884) related the species to C. intermedius Steud.and C. stramineus Nees since, as he stated, both rarely show signs of an elongation of the main axis, however never as prominent as in C. divulsus.Clarke (1908)  More recently Hooper (1972) identified several African collections that approximated to P. divulsus based on the presence of a simply spicate inflorescence.At first they were thought to be introductions of the Madagascan species to the African mainland.Considering the scattered collections of this species from all over tropical Africa and the distinct nutlets (smooth vs tuberculate) and three vs two anthers, the African specimens were described as P. divulsus subsp.africanus S.S.Hooper.The distinction between the two taxa is, however, clear cut and easily observed, so the species level seems more appropriate for the African taxon.Both taxa are poorly known and often unidentified in herbaria.A key and illustrations are included to overcome this problem in the future.The nutlet epidermis of these taxa was studied with SEM to evaluate their position in the Kükenthal (1936) classification.1) were mounted on aluminium stubs using Leit-C.For SEM observation, the material was coated with gold with a SPI-ModuleTM Sputter Coater (SPI Supplies, West-Chester, Pennsylvania, USA).Scanning electron microscope (SEM) images were obtained with a JEOL JSM-5800 LV scanning electron microscope at the National Botanical Garden of Belgium in Meise.

Mature nutlets of representative herbarium specimens (Table
A distribution map of P. divulsus and P. africanus was created with Arcview GIS 3.2.

KEy TO THE SPECIES
1. Nutlets smooth, 1.5-1.9mm long.Pycreus africanus is a rare species known from several remote locations in tropical Africa (Map 1).Most collections are from moist grassland occurring at medium altitudes except the collection in Sierra Leone which is from near the coast.In Ethiopia the species could be confused with P. pauper which can be found in the same habitats (e.g.Robertson in Mooney 7548a & b (K), mixed collection).The latter is also an annual species with a reduced inflorescence and large spikelets and nutlets.However, it differs from P. africanus in having a rather capitate inflorescence, black-tipped glumes and nutlets with elongated epidermal cells as shown in Fig. 1c.
Annual herbs 6.5-38 cm high, with triangular and glabrous culms 0.7-1.1 mm wide.Leaves basal, 0.8-2 mm wide, scabrid near the tip; sheaths pale with many small red dots.Anthela simple and reduced to a terminal spike with 2-4 sessile and suberect spikelets, the lower spikelets often 5-7 mm lower than the others.Bracts 3 or 4, leafy, 1.4-9.8cm long, erect.Spikelets narrowly elliptic, suberect, 4-15 mm long, 2.5-4.4 mm wide with 4-18 flowers; rachilla straight, pale.Glumes oblong elliptic, with a narrow acute tip, 3.1-4.2mm long, 1.1-1.5 mm wide, golden, brownish tinged and with many small red dots, hyaline border wider towards the tip, keel green with 5 nerves; slightly imbricate.Stamens 3, anthers oblong, 0.5 mm long.Nutlets broadly elliptic, 1.5 -1.9 mm long, 1-1.2 mm wide, strongly swollen (nearly round in cross section), black and shiny, the surface smooth; epidermal cells irregular.As Kükenthal (1936) noticed, the nutlets of P. divulsus resemble those of the other members of the section in their wavy aspect.However, SEM pictures from the nutlets of P. divulsus, P. muricatus, P. pauper and P. zonatus clearly show a difference in the shape of the nutlet epidermal cells.Pycreus muricatus, P. pauper and P. zonatus all have strongly elongated epidermal cells and due to this elongation, the tangential walls of the epidermal cells are lifted, resulting in the strongly wavy appearance of the nutlets (Fig. 1a-c).In other Pycreus species, for example P. flavescens, this elongation is less pronounced, which results in narrow transverse frills on the nutlet surface.
In contrast, the nutlet epidermal cells of P. divulsus are isodiametric or only slightly elongated, as already correctly observed by Clarke (1908) (see Fig. 1d, e).Therefore we conclude that the classification of P. divulsus in the 'Zonati' and relationships with the other members of Cyperus (Pycreus) sect.Muricati by Kükenthal (1936) was based on superficial similarities and the name Pycreus sect.Tuberculati should be reserved for P. divulsus and its relatives.Only with exclusion of P. divulsus, Cyperus sect.Muricati becomes available for further use (Art. 52.3 McNeill et al. 2006).Note -The section comprises Pycreus species characterised by a simply spicate inflorescence and large, asymmetrically turgid nutlets (abaxial side most swollen) with a smooth to tuberculate surface.The section is automatically typified by P. divulsus, the only species in the section at the time of its description.

these species are characterised by turgid nutlets with a strongly wavy or muricate surface. In his key, Kükenthal places C. divulsus most closely to C. pauper, which is also an annual species with rather large glumes and nutlets and a reduced inflorescence.
was the first to prepare a detailed infrageneric classification of Pycreus.Pycreus divulsus was put in Pycreus subgenus Reticulati C.B.Clarke, which is characterised by (nearly) isodiametric nutlet epidermal cells, in contrast to his second subgenus Zonati, which has strongly elongated nutlet epidermal cells.At the sectional level Clarke placed P. divulsus together with P. sanguinolentus (Vahl) Nees, P. atronervatus (Boeckeler) C.B.Clarke, P. mundtii Nees and P. atropurpureus C.B.Clarke in Pycreus sect.Vestiti C.B.Clarke, from which it differs in having a completely different habit, inflorescence, different nutlets and glumes.It was Chermezon (1919) who remarked on the difficulties of classifying P. divulsus among the other known species and, based on the unique tuberculated nutlets of the species, he established a new section Tuberculati.

Table 1
Specimens used in the SEM study of nutlet epidermal cells.
PYCREUS SECTION TUBERCULATICyperus (Pycreus) sect.Muricati Kük. was established to unite the Pycreus species with turgid and muricate nutlets(Kükenthal  1936).It can be automatically typified underArt.22.6 (McNeill  et al. 2006)by the type of the name of the species from which the subdivisional epithet was derived, i.e. C. muricatus Kük.Although this section contains C. divulsus, which is the type of Pycreus sect.Tuberculati Cherm., established in 1919, he placed the latter in synonymy.Kükenthal's name, in its original circumscription, should therefore be considered as a superfluous later homonym for sect.Tuberculati(Art.11.4 and 52.1  McNeill et al. 2006).