Additions to the Pantepui pollen flora ( Venezuelan Guayana ) : the Maguire Collection

This work is a pollen-morphological study of various plant species from Pantepui (Venezuelan Guayana), a region with high biodiversity and endemism, where global warming is expected to have a high impact. The study consists of a series of morphological descriptions of selected taxa from the Maguire pollen reference slide collection of The New York Botanical Garden (NYBG). The collection was initiated under the supervision of Senior Curator Bassett Maguire to advance systematic, palynological, and medical studies; today it has become also useful for other disciplines such as paleoecology, paleoclimatology or forensic studies. The aim of this pollen-morphological study is to enhance the database of pollen descriptions and illustrations for identification purposes, to be used in the ongoing paleoecological reconstructions and, eventually, in other types of studies using pollen, particularly from the Guayanan tepui summits.


INTRODUCTION
This paper is part of a series devoted to the pollenmorphological study of vascular plant species from the Venezuelan Guayana (Fig. 1), particularly from the characteristic sandstone tabular mountains (tepuis), initiated by Salgado-Labouriau & Villar (1992) and continued by Rull (2003).The biodiversity and endemism of this region are striking, but the origin and evolution of such exceptional biotic features has been object of intense debate, which is still ongoing (Rull, 2010).On the other hand, the tepuian flora is expected to be seriously affected by relatively rapid biodiversity loss under ongoing global warming.Hence, paleoecological and paleoclimatic studies on this region can provide useful information about biogeographical and evolutionary processes as well as the effects of climate change on the tepuian biota.
Besides the papers mentioned above, which are monographic for the pollen of the Guayana region, the available literature dealing with this subject is scarce and organized taxonomically.Rapateaceae and Asteraceae are the most thoroughly studied families in this sense, although the knowledge of Asteraceae is restricted to some genera of Mutisioideae (Carlquist, 1961;Tellería, 2008;Funk et al., 2009;Ubiergo et al., 2009).Accordingly, the aim of this study, as well as the previously mentioned works, is to enhance the database of pollen descriptions and illustrations for identification purposes, to be used in the ongoing pollen-based paleoecological reconstructions (Rull et al., 2010) and, eventually, in other types of studies using pollen.This work is based on the Maguire pollen reference slide collection, initiated in the forties of the past century by Senior Curator B. Maguire of the New York Botanical Garden (NYBG) to make progress in biological research.Most genera and/or species studied here are endemic to the Guayana region or even to the Pantepui province or a single tepui.

Study area: Pantepui
In the local indigenous language (Pemón), "tepui" means "stone bud", and is the name for the characteristic sandstone/quartzite tabular mountains of Guayana (Fig. 2).They vary in altitude and extension, ranging from around 1100 to 3000 m (typically 2000-2600 m) of maximum elevation, and with a surface of < 1 to > 1000 km 2 (typically 200-500 km 2 ) (Huber, 1995a).The tepui summits are more or less flat and hold unique and specialized life forms and communities, as well as a high diversity and an amazing degree of endemism (Rull, 2009).This biotic singularity led to the creation of the Pantepui biogeographical province, which embraces all the tepui summits above 1500 m elevation (Huber, 1988(Huber, , 1994)).Vascular plants are the better known organisms of Pantepui, with almost 2500 species, of which > 60% are endemic to the Guayana region and > 40% are endemic to Pantepui, including 25% species endemic to a single tepui (Berry & Riina, 2005).Similarly, most tepuian vegetation types are unparalleled worldwide (Huber, 2005).Pantepui is mostly pristine due to its remoteness and inaccessibility; only a few of the tepui summits can be reached by foot after several days of walking and climbing.Indigenous people living in the surrounding lowlands and midlands do not visit the tepui summits because they consider them the home of gods and access is not allowed.On the other hand, there is no potential for commercial profit through activities such as mining, agriculture, cattle raising, etc. (Gorzula & Huber, 1992;Huber, 1995b).Tourism and biopiracy are restricted by severe regulations that, unfortunately, also hinder scientific research (Rull & Vegas-Vilarrúbia, 2008;Rull et al., 2008a).The main threat for the Pantepui biota is global warming that, according to recent estimates, would determine significant biodiversity losses by upward migration and the corresponding habitat loss and fragmentation for many endemic species (Rull & Vegas-Vilarrúbia, 2006;Rull et al., 2008b;Nogué et al., 2009).

MATERIAL AND METHODS
Slides for this study are part of the Maguire pollen reference slide collection preserved in The New York Botanical Garden (NYBG; see http://www.nybg.org/).The collection comprises 3650 preparations of modern pollen representing 153 vascular plant families, of which 11 are non-seed plants.Some preparations include duplicate slides.Most vouchers are deposited in the Steere Herbarium of NYBG and can be viewed on-line (http://www.nybg.org/).The collection was initiated under the supervision of Senior Curator Bassett Maguire (1904Maguire ( -1991) ) (Briceño & Schubert, 1990).The region under study (the Venezuelan Guayana) is indicated by a box.these specimens will undoubtedly surpass the original objectives by serving fields as for example paleoecology, climate change or forensic studies, among others.The breadth of the collection is international in scope with the greatest geographic representation in tropical America, particularly the Guayana region of northern South America.Systematic strengths of the collection reflect Maguire's interest in plant groups with high species diversity or endemism in the Guayana (e.g., Clusiaceae, Gentianaceae, Rapateaceae, and Velloziaceae).Samples for the Maguire collection were mostly obtained from dried or fluid preserved collections housed at NYBG, but also include dried or fresh material as well as prepared slides from other institutions.Pollen grains were chemically treated with KOH, acetolysis, a combination of the two, or were untreated, and mounted in glycerin jelly.The slides are stored in vertical sleeves in a steel cabinet (see Howard & Boom, 1990, Fig. 11).
Measurements for this work have been taken in all the available well-preserved grains; the number of grains used in each case is indicated after the measurements (n=x).Measurements were taken using the photographic software DPXViewer 1.14.9 and a DeltaPix InfinityX camera.A number of species could not have been described because of the absence of suitable pollen grains due to bad preservation.These taxa are listed in the appendix for reference.Taxa are ordered alphabetically by families, following the classification of the Flora of the Venezuelan Guayana (Steyermark et al., 1995(Steyermark et al., -2005)).For each plant species there is a morphological description accompanied by some photographs of the pollen grains found in the slide.The descriptions follow the Rull (2003) style for consistency, and use the standard nomenclature system of Punt et al. (2007).The title of every description summarizes the genus and species, the species authors, the pollen catalogue number, the collector, the collection location, as well as other information present on the label of the slide.Within the description, colpi and ora sizes are expressed as length x width (regarding the direction of the polar axis, in equatorial view), and grain size, as length of the polar axis x equatorial diameter.Also, the more recently accepted name of the species is noted where necessary, as well as the literature where pollen of other species of the same genera from the Venezuelan Guayana are described, if any.The following abbreviations have been used in the text and descriptions: PV, polar view; EV, equatorial view; P/E, ratio of the length of the polar axis (P) to the equatorial diameter (E) (this ratio is the basis of a system of shape classes, Punt et al., 2007).Finally, the photographs are ordered by pollen morphology (monads, tetrads and polyads, and the number and type of apertures  Monads.Isopolar, prolate (P/E = 1.53), amb circular slightly lobate.Tricolporate, zonoaperturate.Ectocolpi long, rounded ends, elliptic (74.8 x 3.7 mm), slightly marginate.Ora fusiform, lalongate (7.6 x 23.6 mm).Exine 3.1 mm thick, thicker at the poles (4.8 mm), tectate, psilate (columellae visible through the tectum).Sexine thicker than nexine.Grain size: 91.5-101.5 x 56.6-69.9mm, n = 11.

Figure 1 .
Figure1.Map of northern South America, showing the approximate extension of the Guayana Shield (in grey) and the Precambrian sandstones and quartzites of the Roraima group (in black), on which the tepuis are modelled(Briceño & Schubert, 1990).The region under study (the Venezuelan Guayana) is indicated by a box.