Download Introduction Poaceae (R.Br.) Barnh. is the fourth

Introduction
Poaceae (R.Br.) Barnh. is the fourth largest family of flowering plants. It includes
about 700-800 genera and 10,000-11,000 grass species distributed worldwide (Clayton &
Renvoize 1986, Watson & Dallwitz 1999, Tropicos 2011). Grasses occur in nearly all the
ecosystems and habitats of the world (Clayton & Renvoize 1986, Ture & Bocuk 2007,
Osborne et al. 2011) and provide cover to nearly a fifth of the land surface (Shantz 1954,
Arabaci & Yildiz, 2004, Brooks et al. 2004). Several studies have dealt with spatial and
temporal frame for the origin and diversification of grasses and allied plant types.
Attempts have been made to construct the paleo-ecological and paleo-biogeographical
maps and paleo-historical calenders to trace major evolutionary events that lead to
differentiation of various clades first among families of the order Poales and later
between and within families of the graminoid clade. Fossil evidences coupled with
comparative molecular genomics and physiological status of present day species have
been utilized to reconstruct the evolutionary history and understand the past and present
distribution of various groups of grasses. Bremer (2000) postulated the origin of order
Poales in the mid-Cretaceous (115± 11 mya). Early differentiation of Poales has been
located in Southern continents breaking away from the Gondwanaland (Dahlgren et al.,
1985). Fossil pollen referable to graminoid families Poaceae and Restionaceae has been
recovered from the Late Cretaceous (>65 mya) which point to evolution of grasses by this
time (Linder, 1987). But, the typical spikelets that mark the origin of the earliest grasses
have been reported no earlier than 55 mya at Paleocene-Eocene transition in the
Coenozoic (Crepet and Feldman, 1991). Taxonomic diversification and geographic
diversification occurred during the Eocene in several phases beginning with the crown
node of bambusoid grasses (53mya) and continuing with the pooid (47-38 mya),
chloridoid (35-25mya) and panicoid (26mya) groups (Klootwijk et al. 1992, Kellogg
2001, Bouchenak-Khelladi et al. 2010). With their origin in the southern land masses,
grasses are believed to have spread to Eurasia via the Indian land mass (Klootwijk et al.
1992).
Grasses comprise a remarkable group of plants with unmatched economic and
ecological importance. Their relevance and importance to mankind can hardly be over
emphasized. Ever since the origin of agriculture, grasses have occupied the centrestage of
human subsistence and economy. All our cereals and millets are grasses that have been
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Introduction
cultivated since millennia. Sugarcane, the main source of sugar around the world also
belongs to the family Poaceae. In fact, human civilization developed only after successful
cultivation of cereal and fodder grasses of various kinds. Apart from food and fodder,
several grasses are used for extraction of aromatic oils and scents (Kaul & Vats 1998,
Khanuja et al. 2005, Kim et al. 2005, Bhuiyan et al. 2008, Sujatha, 2010). Grasses also
provide green cover to our lawns and landscape for tourism and sports. Their use in
handicraft and cottage industry is well known.
The ecological role of grasses is equally significant. They constitute the most
ubiquitous component of the terrestrial vegetation of the entire globe ranging from
tropical to the polar and rain forests to the arid. Their roots and creeping rhizomes and
stolons act as efficient soil builders and soil binders. Thus, grasses act as pioneers in plant
succession and prepare the ground for soil and overground flora and fauna. In terms of
abundance and frequency, they outnumber manifold any other group of plants.
Vegetation types having a stratified structure topped by tree canopies harbour low
growing grass species that occupy the understorey and the ground strata. But, open and
exposed vegetation zones are dominated by tall grasses. These landscapes called
grasslands are known by colloquial terms in different parts of the world. The open and
flat landscapes of southern Africa overgrown with a mixture of small grasses and low
scrub are called ‘Velds’ which is the English rendition of the Afrikaan word for ‘field’.
Grasslands developing in rain shadows of mountains in North America are called
‘Prairies’ literally meaning ‘meadows’. Generally, a ‘Prairie’ does not have enough
rainfall and soil moisture to support growth of trees leaving the terrain open for growth of
tall grasses and the grasslands. Grasslands developing in the semiarid and continental
climate marked by extremes of summer high (upto 400C) and winter low (down to -40oC)
temperatures and a profusion of shorter grasses of semiarid zone are called ‘Steppes’.
They occur in cold continental climate of Eastern Europe and Central Asia but ‘Steppe
like’ grasslands are also encountered in semiarid and subtropical regions of the world
marked by a moderate rainfall and high evapotranspiration. In India, the semiarid land
fringing the Thar Desert supports a ‘Steppe-like’ grassland. However, a majority of
grasslands of India are ‘Savannas’ which are defined as grassland ecosystems with a
remarkable representation of trees that dot the landscape but are so widely spaced that
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Introduction
they leave large gaps in the canopy for sunlight and luxuriant growth of hardy grasses.
Thus, Savannas are ecosystems that have a more or less continuous grass cover but
discontinuous tree cover (Scholes and Archer 1997).
Despite comparatively recent origin and diversification, grasses have come to
have cosmopolitan distribution and dominance in some of the ecosystems outwitting even
trees and other elements of the ground flora. Several attributes of grasses have
contributed to their wide distribution, perpetuation and occasional dominance in some
ecosystems called the grasslands. Among growth characteristics is a dense and fibrous
root system that explores and exploits soil water and nutrients more actively than
arborescent elements (Partel and Wilson 2002). Apart from an efficient utilization of soil
resources, grasses, particularly in the tropics, have deep seated buds below the ground
surface safe from forest fires which obliterate woody samplings (Mouillot and Field,
2005). Apart from ecology, grasses have a highly efficient reproductive strategy
combining contiguous spread by vegetative means and non-contiguous dispersal to new
locations through sexual diaspores. Grasses have higher survival and biomass
productivity due to the existence of alternative C4 route of carbon assimilation in hot
tropics that induce photorespiration in C3 plant species. The C4 grasses show a syndrome
of anatomical and biochemical adoptions that help to minimize photorespiration and fix
CO2 precisely at anatomical sites of fixation (Sage, 2004, Edwards et al. 2010). The C4
cycle has allowed grasses to spread in several drier tropical and subtropical habitats
(Osborne & Freckleton 2009, Edwards and Smith, 2010). In humid Savannas, C4 grasses
reach high levels of biomass production.
Besides ecology, grasses possess tremendous taxonomic significance. Owing to a
peculiar and distinctive morphology, the grass plant is a taxonomic novelty. As such,
grasses have always attracted the attention of naturalists and plant systematics. Landmark
contributions of Nash (1903), Hitchcock (1914, 1920 & 1933), Stebbins (1956), Bor
(1960), Gould (1968) and Gould and Shaw (1983) provided a firm foundation to grass
systematics. Thereafter, information on diversity and distribution of grasses has steadily
increased by the noteworthy contributions of Clayton & Renvoize (1986) and Watson &
Dallwitz (1992). The establishment of Grass Phylogeny Working Groups (GPWG I & II)
have provided grass systematists of the world the much needed forum for guidance and
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Introduction
exchange of information. Worldwide checklists of grass species with notes on
phytogeographic distribution have become a point of reference for researchers across the
globe. In their systems of classification of the family Poaceae, GPWG I (2001) and
GPWG II (2012) have recognized twelve subfamilies instead of only five or six by
relocation of genera and splitting of taxa. Evidences for this phylogenetic classification
have been drawn not only from morphology but also from molecular data or
combinations of both the approaches (Salamin et al., 2002, Peterson et al. 2012, Jones et
al. 2014). Within subfamilies, large and complex genera have been revised (Saarela et al.
2003, Spangler 2003, Molina & De Agrasar 2004, Finot et al. 2005, Zuloaga & Morrone
2005, Paszko 2012, Baum et al. 2014, Veldkamp 2014). Apart from reclassification,
recent studies have brought to light possible evolutionary changes that have lead to the
characteristic grass morphology and anatomy. Such studies have brought to light the
phylogenetic route and temporal frame for such fundamental questions of grass
organography as development and organization of the spikelet (Kellogg, 2001), petaloid
nature of the lodicules (Ambrose et al. 2000) and origin of the C4 anatomy and
physiology (Gaut & Doebley 1997, Kellogg, 2001, Christin et al., 2008, Edwards and
Smith, 2010).
Owing to their cosmopolitan distribution and a finely timed phenology, grasses
have emerged as a model group of biological indicators for climatic and environmental
change. Grass species exhibit several clearly defined phenophases in their phenological
cycle. Each of the phases namely the bud burst, the boot formation, inflorescence
emergence, fruit set and disarticulation of the diaspores are precisely timed events in the
yearly cycle. Several studies have attempted to utilize grasses as models of environmental
change through an empirical delimitation of parameters controlling these phenological
shifts (Buzzaz, 1991; Thornley and Cannell, 1997; Steinaker et al., 2010). A high degree
of seasonal and habitat specificity make grasses an ideal choice as environmental
indicators.
In India, two important factors lend a place of privilege to grasses and the grass
flora. Firstly, the tropical climate of the country is mainly responsible for creation and
perpetuation of grasslands. Dabadghao and Shankarnarayan (1973) argued that large
chunks of Indian territory traditionally classified as forests are actually grasslands. The
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Introduction
authors identified five types of grass covers for the country and also listed out the forest
types whose physical boundaries coincide with these grass covers. The authors also
argued that the grasslands of India are edaphic rather than vegetational climaxes and that
they are perpetuated through continuous biotic disturbances that disrupt the tree canopy
and do not allow these grasslands to succeed into woodlands. The second important
factor for the predominance of grasses is the agrarian economy heavily dependent upon
cultivation of cereals and millets for human food and animal fodder. Agricultural fields
throughout the territorial expanse of the country are simply monocultures of about a
dozen grass species. Within the country, grasses assume even greater importance in
regions like Punjab which have a land use heavily biased towards intensive agriculture.
Despite overwhelming significance of grasses and grasslands in the country and
an upsurge in grass systematics the world over, India has been categorized as a ‘seriously
undercollected’ country as far as diversity and systematics of grasses is concerned
(Kellogg, 2006). Nevertheless, an enthused interest in grasses throughout the world has
given an impetus to research on different aspects of Indian grasses. Given the fact that
cultivated grass species constitute the mainstay of our agrarian economy and wild grasses
dominate our subtropical/tropical ecology, this is a significant development. Research
publications have reported new species and genera (Ravi et al. 2001, Potdar et al. 2003,
Salunkhe and Potdar 2004, Sunil and Pradeep 2005, Kabeer and Nair 2007, Kiran Raj
and Sivadasan 2008, Yadav et al. 2010, Raole et al. 2011, Kiran Raj et al. 2013). Besides
taxonomy, research in grasses has recently been extended to other aspects including
ecology (Yadava 1990, Kunhikannam, 2008, Reshi et al. 2009), physiology (Nath, 2004),
reproductive biology (Kaushal et al. 2004, 2005), molecular biology and genetic diversity
(Chandra et al., 2004, Saxena & Chandra, 2006) and dispersal strategies (Sharma et al.
2010).
Punjab, the area of present investigation, has a predominance of grasses both in
the wilderness as also the cultivated fields. It is practically a ‘grassland of cultivated
species’ or a ‘cultivated grassland’. Besides cultivated fields, grasses constitute the
dominant elements of rangeland vegetation and ecology of the region. But, grasses have
not been given sufficient attention in floristic compilations of the region. Some of the
earliest works made no mention of the group (Bamber 1916, Kashyap 1936). Others have
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Introduction
given only an alphabetic list of species with sketchy descriptions (Stewart 1869, Sabnis
1940, Nair 1978, Sharma & Bir, 1978). It is only in the work of Sharma & Khosla (1989)
that grass species were given a systematic treatment.
Our research group has initiated work on systematic inventorization, taxonomic
description and characterization of the grass species of Punjab and adjoining hills
according to the latest format and systems of classification (GPWG I, 2001 and GPWG
II, 2012). We have made some headway in grass systematics by preparing an updated
conspectus of grasses (Soodan et al. 2012) and taxonomic descriptions of some hitherto
undescribed species (Kumar and Soodan 2013). Besides taxonomic update and species
characterization, the group is actively pursuing phytosociology (Soodan et al., 2009) and
dispersal and facilitated propagation of grass species of the region (Soodan et al., 2012).
The present work was planned with the following objectives in mind.
1.
To explore the three plain regions (Doabs) of Punjab along with neighbouring
hills for diversity of grasses through intensive field surveys and collections.
2.
To prepare an updated conspectus of grasses of Punjab through a comparative
study of past reports and present collections. A possible outcome of this study
would be some new reports of grass species from the region.
3.
To identify and undertake detailed taxonomic description of the collected species
according to the latest formats of descriptions available online at ‘GrassBase-the
Online World Grass Flora’ at http://www.kew.org/data/grasses-db. html. The
descriptions are maintained by Clayton, WD, Vorontsova, M.S., Harman, KT,
Williamson, H. (2006 onwards)’ for The Board of Trustees, Royal Botanical
Garden, Kew, U.K.
4.
To complement the textual descriptions of the past compilations and past work
with spikelet formulae and spikelet diagrams by appropriate modifications
required for various groups of grasses. The sources for basic scheme of these
diagrams and formulae are given in the third chapter of this thesis.
5.
To work out etymological derivation and grammatical structure of generic names
and specific epithets of grass species for ready reference of grass systematists and
students. A note on the etymology of each species would provide useful hints
about the nature of the grasses encountered in the field.
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Introduction
6.
To classify grass species of the study area according to the latest scheme of the
grass classification proposed by Grass Phylogeny Working Group I (2001) and
modified by GPWG (2012). A user friendly key to various taxa down the
taxonomic hierarchy is also an objective of the present study.
7.
To provide information about seasonal distribution and habitat preference of
grasses of the region for ready reference by students and agrostologists interested
in the academic and applied study of grasses of the region. Another objective was
to decipher the types of grass covers and their annotation to the accepted
classification of grass covers of the country (Dabadghao and Shankranarayan,
1973).
8.
To develop the departmental herbarium into a nodal centre of reference for
grasses of the region through collection and preservation of herbarium sheets of
the collected specimens.
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