Characterization of lemma and palea in nine different species of Eragrostis (Poaceae)

Eragrostis, the largest genus in tribe Eragrostideae has 36 species in India and with 406 species in the world. The present study investigates the morphological and micromorphological variations of lemma and palea in nine species of the Eragrostis, collected from Panchmahal and Dahod districts of Gujarat. Qualitative and quantitative features of microharis, and epidermal cells in the different regions, apex middle and base of lemma and palae has been observed. Apart from this, undulation patterns also play a key role in species identification. Two major types of undulation pattern ∩ and Ω have been observed in the studied species. The present study concludes that, different types of microhairs, size and shape of epidermal cells and its undulating pattern can be significantly used in delimitation of Eragrostis with the help of all the qualitative and qualitative characteristic features it was possible to prepare a dichotomous key to identify the nine different species of Eragrostis.


Introduction Introduction Introduction Introduction
Eragrostis Wolf the largest genus having 406 species (POWO, 2021) belong to subfamily Chlorideae of the tribe Eragrostidae in family Poaceae. These species occur in tropical, subtropical and warm temperate regions throughout the world (Clayton and Renvoize, 1986;Peterson et al., 1993Peterson et al., , 2001Van den Borre and Wasten, 1994). Within in India 36 species (Karthikeyan et al., 1989) and in Gujarat 14 species (Shah, 1978) were recorded. Eragrostis the species limits are often overlapping and few agrostologists have attempted to work out on suitable phylogenetic scheme. Based on spikelet disarticulation at maturity, Clayton et al. (1974) and Amarasinghe and Waston, 1990). Apart from leaf, characters of floral bracts including lemma and palea are also very important to know the phylogeny and evolutionary relationship between taxa. Micromorphological features useful for the identification and characterization of tribes and subfamilies, for example absence of micro hairs is characteristic in Pooideae (Clayton and Renvoize, 1986). Micro and macro characters have taxonomic significance within genera, as in the case of micro hairs in Eragrostis (Amarasinghe and Waston, 1990), being especially useful for the characterization of the larger groups, particularly sub families and tribes.
The present study aims to characterize Eragrostis at the species level, based on characters of micromorphological characteristic features of lemma and palea.

Materials and Methods Materials and Methods Materials and Methods Materials and Methods
Total nine species of Eragrostis were collected from the grasslands of Baria and Godhra forest division of Panchmahal districts. 20-25 individuals of species were gathered and identified Lemma and palea from the lowest floret in the spikelet were carefully separated, washed with distilled water to remove any dust particles adhering to it and used for observations from the apical, middle and basal portions of each part. Observations were carried out first with a stereo microscope and then under light microscope. Terms described by Ellis (1979) was followed for description of micromorphological features. The different spikelets and its parts were photographed with Leica DME microscope.

Results Results
Results and Discussion and Discussion and Discussion and Discussion Lemma and palea of Eragrostis Length of lemma is more than palea in all studied species, except Eragrostis japonica and Eragrostis tenella. A variation in the number of veins on the surface of glumes have been distinctly noted. In Eragrostis pilosa the surface of glumes are smooth with an absence of veins while in all the other species a single the centre of the lemma and palea and in Eragrostis ciliaris the number of veins vary form 1 to 3.
Lemma of Eragrostis tenella shows glabrous surface while others with scrabous surface. Apex of lemma obtuse in all the species, except Eragrostis nutans and Eragtostis unioloides with acute apex. Shape of upper and lower glumes ovate except Eragrostis ciliaris with lanceolate glumes. All the Eragrostis species had an acute apex in both glumes. Lemma and palea of nine species showsn in Figure 1.
Unicellular or bicellular trichomes were prominently seen on glumes. Nerve hairs a common feature noted in Eragrostis is characterized by being completely covered by the hairs directed towards the apex.
Significant variation has been observed in the density of the hairs. Variations were also found in the apex, basal regions, nerve and marginal hairs. Characteristic features and terminology used in the present study are as per terminology of the grass inflorescence morphology in Grassbase (Clayton et al., 2006), Ausgrass (Simon and Alfonso, 2011) and Grass genera of the World (Watson and Dallwits, 1992). A total of 45 characters were assessed for variability (12 for grass inflorescence and 33 for lemma micromophology). Characteristic terminology of lemma micromorphology has been followed as per Ellis (1979).    (Figure 3 A, B, C).
Palea: Palea: Palea: Palea: On nerve spiny, thick walled, rough, unicellular trichomes with broad base. Multicellular trichomes are small compared to one long cell of palea and base is rounded (Figure 2 A).

Eragrostis ciliaris Eragrostis ciliaris Eragrostis ciliaris Eragrostis ciliaris
Lemma: Lemma: Lemma: Lemma: Nerve hairs are not long as of palea. They are unicellular, narrow with broad base, pointed tip, direction towards apex of the lemma, bulbous hairs found at the base region (Figure 2 D). At margin of the lemma there are many unicellular hairs are present which have pointed tip and broad base. Density is more (Figure 2 B, C).
Palea: Palea: Palea: Palea: Broad, long, unicellular hairs rigidly spreading at maturity. Spiny hairs with bulbous base thick walled vary in length arise from the nerve region, long hairs arranged loosely, direction towards the apex with more density (Figure 2 D, E). The short unicellular hairs found on the all over surface, tips are pointed, narrow and long and thin walled. The base is more rounded, density is more at the apex region (Figure 2 F).

Eragrostis japonica Eragrostis japonica Eragrostis japonica Eragrostis japonica
Lemma: Lemma: Lemma: Lemma: Unicellular, small, thin-walled margin hairs and direction towards apex region. Bulbous hairs are found on the surface, density is less. Apex hairs found arranged parallel (Figure 3 E, F, G).
Palea: Palea: Palea: Palea: Spiny, thick walled, rough, unicellular trichomes are present on nerves directing towards the apex of palea. But density is very less, base broad arising from the nerve region. Multicellular bulbous hairs found on the surface with less density ( Palea: Palea: Palea: Palea: At apex region, 2-3 hairs, thick walled, unicellular, pointed tip, spiny nerve hairs are present, density more, arise from the nerve region, direction towards the apex, having broad base. Bulbous, multicellular hairs are present at the base region. Some globular trichomes with globular tip are also present but density is very less.

Eragrostis tenella Eragrostis tenella Eragrostis tenella Eragrostis tenella
Lemma: Lemma: Lemma: Lemma: Long ciliate, broad, unicellular spiny prickles with bulbous base thick walled vary in length arise from the nerve region. The short unicellular, narrow and long, thin walled, pointed broad tip hairs found on the all over the surface. The base is more rounded and density is more at apex region (Figure 2 M, N).
Palea: Palea: Palea: Palea: Nerve hairs are long, ciliate along the keels, rigidly spreading at maturity, very broad, unicellular, spiny hairs with bulbous base, thick walled and vary in length (Figure 2 O, Q). Density of long hairs is more, arranged loosely and direction towards the apex is not necessary. The short unicellular prickles found on the all over the surface, broad tip which is pointed, narrow, long and thin walled (Figure 2 P). The base is more rounded, density is more found more at the apex region. Multicellular bulbous hairs are also present at the basal region, the cells have rounded cap and long middle region the base is bulbous scattered at the basal region and density is less (Figure 3 M, N).  Eragrostis tremula Eragrostis tremula Eragrostis tremula Eragrostis tremula Lemma: Lemma: Lemma: Lemma: Bulbous hairs are found on the surface with less density. At nerve hairs are absent but 1-2 are found at apex region.
Palea: Palea: Palea: Palea: Nerve hairs are long, narrow, base not much broad, unicellular, pointed tip, direction towards apex of the palea, thin walled, smooth surface. Bulbous hairs found at the base region. At the apex region, hairs are found in cluster and are long, narrow with smooth margin and thin wall arise from the tip of the palea ( Table 1 and 2. Cells present on the surface of lemma are smaller than palea except lemma of Eragrostis tremula had more length than the palea.

Variation in undulation patterns
By means of light microscopy the surface undulated patterns of epidermal long cell walls in the lemma and palea can be divided into two distinctly different types as observed in Setaria (Houyuan et al., 2009). The epidermal cell walls are having either Ω shaped undulation (undulation rounded, wider towards the apex and narrow at the base) or ∩ shaped undulation. Both these types further can produce branching sub ordinate types based on the degree of undulations as Ω I, II, III and ∩ I, II, III. The depth and width of the undulations vary in the different studied species depending on which in some the undulations appear very compact, while in some it is scare as seen very distinctly in the lemma of E. viscosa and E. ciliaris. All types of undulations seen in Figure 7.
∩ shaped undulation in the palea is very prominent in E. pilosa. In the apex and basal region, the undulation is more or less same. It does not become narrow at the base.
The size of the cells at the apex, middle and base of the lemma varied in a species within the length and width. The length of the lemma was maximum in E. tremula and E. unioloides while it was minimum in E. japonica and E. nutans.
Similarly, size of the cells showed variation in the three different regions (apex, middle and basal) of the pale of the species and within species. The size of palea was maximum in E. unioloides and minimum in E. nutans. There was a significant variation in the characteristic features of microhairs.
One of the main problems with micromorphological studies is to determine the optimal site of observation. The lemma shows variations in the expression of micromorphological characters within its apex, base and margins, whereas the palea varies mostly near the apex and in some cases in the wings.
The analysis of the epidermal micromorhology of lemma and palea reveals considerable variation in the nine species of Eragrostis. These characters are valuable for systematic studies in Poaceae.
Based on the different micromorphological variation observed in the lemma and palea diagnostic key has been prepared which would facilitate in the identification of the different species.