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Pleione 8(1): 55 - 67. 2014. ISSN: 0973-9467© East Himalayan Society for Spermatophyte Taxonomy

Taxonomic significance of petiole anatomy of Sterculiaceousspecies distributed in Northeast India : Part I

Sonia Mitra and Debabrata Maity1

Taxonomy and Biosystematics Laboratory, Department of Botany, University of Calcutta,35, Ballygunge Circular Road, Kolkata – 700 019, W.B., India

1Corresponding author: [email protected]

[Received 27.04.2014; Revised 03.06.2014; Accepted 04.06.2014; Published 30.06.2014]

Abstract

Petiole anatomy has undoubtedly played immense role in plant systematics and has solvedmany taxonomic problems. The present study deals with the analysis of petiolar anatomicalfeatures of 14 species of Sterculiaceae out of 25 species distributed in the north-eastern statesof India. The studied species include Eriolaena hookeriana Wight & Arnott, Firmiana colorata(Roxburgh) R. Brown, Helicteres hirsuta Loureiro, Heritiera dubia Wallich ex Kurz, H.macrophylla Wallich ex Kurz, H. papilio Beddome, Melochia corchorifolia Linnaeus, Pentapetesphoenicea Linnaeus, Pterospermum rubiginosum B. Heyne, Pterygota alata (Roxburgh) R.Brown, Reevesia pubescens (Masters) Malick, Sterculia foetida Linnaeus, S. guttata Roxburghand S. lanceifolia Roxburgh. The study emphasized on the number and arrangement of petiolartraces along with the nature of accessory bundles, if present; the number and arrangement ofmucilaginous cavities, their pattern of distribution within the pith or cortex or both. All thesecharacteristics serve significant role in delimitation of taxa. Significant changes in the vasculaturepattern have been noticed throughout the length of the petiole; but three basic zones, proximal,middle and distal have been taken into account for the comparative investigation. However, thestable zone which can be put forward as a taxonomic marker is the proximal part. Many of thestudied species are economically as well as medicinally imperative. These anatomical featuresare important in identification of these species in crude condition. This study is also useful inidentification of the species in their non-flowering state.

Key words: Sterculiaceae, north-east India, petiole anatomy, accessory bundles, mucilaginouscavities, taxonomy.

INTRODUCTION

Anatomical data have long been widely used in plant systematics for recognition and evaluationof taxonomic status as well as relationships of taxa of flowering plants (Stuessy 1990). Thestudy of petiole anatomy has achieved much attention among the taxonomists and anatomistsfor solving several taxonomic problems as it provides many useful and stable characters(Grew 1675; Howard 1962, 1979). However, the petiolar anatomical studies of Indian membersof Sterculiaceae have been neglected and very few scattered reports are available, mostlyas a part of other studies (Metcalfe & Chalk 1950; Hussin & Sani 1998).

The anatomical study of Sterculiaceae in general had been done long back by Metcalfeand Chalk (1950), however, very little information is available on Indian members, particularlyon foliar architectural aspects (Mitra & Maity 2013). Thus there still exists a gap that needs

to be filled up, especially in respect to the petiolar anatomical studies. In India,Sterculiaceae comprises of nearly 69 species spread over 20 genera and about 25 speciesare distributed in north-east India (Malick 1993; Paul & Roy 2013) out of which the petiolaranatomical analysis of 14 species have been carried out. The present study is an attempt toevaluate the taxonomic significance of petiolar anatomical features of the studied species intheir proper and correct identification, particularly in non-flowering condition.

MATERIALS AND METHODS

Materials:Twigs and mature leaves were collected from different states of North East India viz. WestBengal (Darjeeling district), Sikkim, Assam, Meghalaya, etc. A list is provided belowcomprising of the studied specimens (Table - 1). Portions of petiole were preserved in FAA[5 ml Formaldehyde (40 %) : 5 ml Glacial Acetic Acid : 90 ml Alcohol (70 %)] for furtherdetailed anatomical studies. Proper identification of specimens were carried out with thehelp of relevant literatures (Masters 1874; Malick 1993) and even matched with earliercollections deposited at CUH and CAL. All voucher specimens are deposited at CUH.

Methods:Serial transverse cross-sections of studied materials were executed at proximal, middle anddistal parts of petioles. In case the petioles were too small, sections were made through outtheir length. 2 % Safranine was used to stain the selected thin sections and then mounted in10 % Glycerin. Standard procedures for the study of anatomical features for preservedmaterials were employed (Johansen 1940). Conventional double staining procedure wasalso adopted in specific cases. Illustrations of anatomical features were done under mirrortype Camera Lucida.

Table – I. List of studied species with respective voucher specimens

56 Taxonomic significance of petiole anatomy of Sterculiaceae

Name of the studied species Collection details (CUH)

Eriolaena hookeriana Wight & Arnott Mitra 20053; Mitra 20055; Maity 20056

Firmiana colorata (Roxburgh) R. Brown Maiti 20049; Maiti 20050; Biswas 20052, Biswas20054

Helicteres hirsuta Loureiro Maity 20051; Mitra 20063; Mitra s.n.

Heritiera dubia Wallich ex Kurz Mitra 20058; Mitra s.n.; Maity s.n.

Heritiera macrophylla Wallich ex Kurz Maity 20049; Mitra 20050

Heritiera papilio Beddome Mitra 20060; Maity s.n.; Mitra 20062

Melochia corchorifolia Linnaeus Maity 20058; Maity 20059; Mitra 20061

Pentapetes phoenicea Linnaeus Mitra & Maity 20004; Mitra & Maity 20044

Pterospermum rubiginosum B. Heyne Maity 20054; Mitra s.n.; Mitra 20057

Pterygota alata (Roxburgh) R. Brown Mitra & Das Das 20023; Das Das & Maity s.n.;Mitra 20046

Reevesia pubescens (Masters) Malick Mitra 20054; Mitra s.n.; Maity s.n.

Sterculia foetida Linnaeus Mitra & Saha 20039; Mitra & Maity 20024; Maitys.n.

Sterculia guttata Roxburgh Maity & Saha s.n.; Mitra & Maity 20005;Mitra s.n.

Sterculia lanceifolia Roxburgh Mitra 20016; Das Das & Mitra s.n.; Mitra 20047

Fig. 1. A1-G

1: Diagrammatic representation of transverse section (T.S.) of proximal part of petioles: A

1.

Eriolaena hookeriana; B1. Firmiana colorata; C

1. Helicteres hirsuta; D

1. Heritiera dubia; E

1. H.

macrophylla; F1. H. papilio; G

1a & G

1b. Melochia corchorifolia; A

2-G

2: Diagrammatic representation

of T.S. of middle part of petioles: A2. Eriolaena hookeriana; B

2. Firmiana colorata; C

2. Helicteres

hirsuta; D2. Heritiera dubia; E

2. H. macrophylla; F

2. H. papilio; G

2a, G

2b& G

2c. Melochia corchorifolia.

A3-G

3: Diagrammatic representation of T.S. of distal part of petioles: A

3. Eriolaena hookeriana; B

3.

Firmiana colorata; C3. Helicteres hirsuta; D

3. Heritiera dubia; E

3. H. macrophylla; F

3. H.papilio;

G3a

& G3b

. Melochia corchorifolia.

Sonia Mitra & Debabrata Maity 57

OBSERVATIONSThe petiolar anatomical features of the studied species show diverse organizations, however,certain characteristics are more or less alike in all of those. Such similar aspects are therebydiscussed in general.

All the vascular bundles are collateral and open. The number of vascular bundle variesfrom one (Fig. 1. D

1-D

3,F

1-F

3) to numerous (Fig. 2. C

1, E

2). Those may either be arranged in

a semi-lunar (Fig.1. G1b

) or more or less circular fashion (Fig. 1. A1). The shapes of each

vascular bundle are either crescent (Fig. 1. A2), or semi-lunar (Fig. 1. C

1) or more or less

triangular (Fig. 2. C3, E

2) and their sizes vary accordingly. All the vascular bundles are provided

with bundle sheath except the proximal part of Pterospermum rubiginosum (Fig. 2. B1).

Bundle sheath is sclerenchymatous and present in patches in all the studied species (Fig. 1.A1).

However, the mid-petiole of Sterculia lanceifolia shows a thick continuous layer of bundlesheath (Fig.2. G

2). Xylem layer appears to be continuous (Fig.2. B

2) to dissected (Fig.2. C

2),

whereas the phloem layer is continuous throughout. Phloem rays are very wide in general(Fig.1. D

2), though, in few cases the ray cells are quite narrow (Fig.2. F

1). Number and

arrangement of mucilaginous cavities also varies significantly from species to species. It variesfrom single (Fig.2. B

1) to numerous (Fig.2. D

1) and distributed either in pith (Fig.2. E

2) or

cortex (Fig.2. D2) or in both (Fig.2. E

1). These may be present randomly (Fig.2. D

1) or in a

more or less circular pattern (Fig.2. D2). Their shapes are almost alike, spherical to ovoid.

As the studied species display assorted features, it is necessary to have a clear idearegarding the vasculature of each individual. For enhanced perceptive a comparative table isprovided to assess the differences of the petiolar anatomical features in the three regions(proximal, middle and distal) of studied species (Table – 2).

DISCUSSION

Comparative analysis of petiolar anatomical features in the studied species revealed thediverse characteristics those proved to be significant in their better and proper identification,especially in non-flowering phase of life. The data recorded are useful to distinguish thestudied species because each of them show unique diverse anatomical characters which arediagnostic, for example, number and arrangement of vascular bundles and accessory bundles,nature of bundle sheath, number and distribution of mucilaginous cavities, etc. Manyresearchers have utilized petiolar anatomical features in taxonomic interpretation of manyplant species, genera and even families (Grew 1675; Metcalfe & Chalk 1950; Fisher 1985;Illoh 1995; Shaheen 2006, 2007; Heneidak & Shaheen 2007; Mitra & Maity 2013).

All the studied species have well-developed pith, except the proximal part of Reevesiapubescens and Sterculia lanceifolia where the vascular bundles completely occupy thepith (Fig.2. D

1& G

1).Thus the pith becomes inconspicuous in both cases.

Among the studied species a collenchymatous hypopdermis is observed only inFirmiana colorata throughout the petiole. Thus this particular species is distinct from theothers in this respect (Fig.1.B

1-B

3).

One of the most interesting findings of the present study is the taxonomic importanceof accessory bundles. The number, arrangement and even the place of origin of accessorybundles varies from species to species and thus can be taken into account for the systematicanalysis. In the specimens undertaken for the investigation the number of accessory bundlesvaries from one (Fig.1. D

1) to numerous (Fig.2. C

3, E

3). Those may either be present

throughout the petiolar length (Fig.1. D1, D

2 & D

3) or in any one zone, middle or distal (Fig.2.


Fig. 2. A1-G

1: Diagrammatic representation of transverse section (T.S.) of proximal part of petioles: A

1a& A

1b. Pentapetes phoenicea; B

1. Pterospermum rubiginosum; C

1. Pterygota alata; D

1. Reevesia

pubescens; E1. Sterculia foetida; F

1. S. guttata; G

1. S. lanceifolia; A

2-G

2: Diagrammatic representa-

tion of T.S. of middle part of petioles: A2a

& A2b

. Pentapetes phoenicea; B2. Pterospermum rubiginosum;

C2. Pterygota alata; D

2. Reevesia pubescens; E

2. Sterculia foetida; F

2. S. guttata; G

2. S. lanceifolia;

A3-G

3: Diagrammatic representation of T.S. of distal part of petioles: A

3. Pentapetes phoenicea; B

3.

Pterospermum rubiginosum; C3. Pterygota alata; D

3. Reevesia pubescens; E

3. Sterculia foetida; F

3.

S. guttata; G3. S. lanceifolia


B3, G

2) or two, middle and distal (Fig.1. C

2 & C

3) regions of the petiole. The bundles

are formed by the branching of main petiolar traces. The number of accessory bundles oftenincreases by either repeated branching of pre-existing accessory bundles or even furtherbranching of the main petiolar traces. On the other hand, the number may decrease either byfusion of pre-existing accessory bundles or fusion of accessory bundles with the main petiolartraces. However, accessory bundles are totally absent in Eriolaena hookeriana (Fig.1. A

1-

A3), Melochia corchorifolia (Fig.1. G

1a-G

3b), and Pentapetes phoenicea (Fig.2. A

1a-A

3)

throughout the length of their petioles. Again, in the proximal part of Helicteres hirsutathere is no sign of any accessory bundle (Fig.1. C

1) but the middle and distal parts have one

and three bundles respectively (Fig.1. C2&C

3). Similarly, the distal part of Pterospermum

rubiginosum is with only one accessory bundle though the proximal and middle parts aredevoid of the same (Fig.2. B

1&B

2). Single accessory bundle is also seen in the mid-petioles

of Reevesia pubescens and Sterculia lanceifolia. In both the proximal part are withinconspicuous pith due to the presence of vascular bundles at the center (Fig.2.D

1&G

1).

Single accessory bundle is also observed in Heritiera dubia throughout its petiolar length(Fig.1. D

1-D

3). Numerous accessory bundles are seen in Heritiera papilio (Fig.1. F

1-F

3),

Pterygota alata (Fig.2. C3) and Sterculia guttata (Fig.2. F

3). Heritiera macrophylla

(Fig.1.E1-E

3) is with four accessory bundles at proximal part which becomes eight by division

at middle and again reverts to four at distal part by fusion. In Firmiana colarata (Fig.1. B1-

B3) proximal part is with two accessory bundles, which by fusion becomes single in the

middle and again at the distal part by division and further branching of main petiolar tracemany such accessory bundles are formed. Similarly, in Sterculia foetida (Fig.2. E

1-E

3) two

accessory bundles are present at the proximal part, which becomes one at the middle byfusion and again by division forms a complex configuration at the distal end. Thus, fusion andfission of the accessory bundles are the frequent events throughout the petiolar length and isalso seen in Helicteres hirsuta, Heritiera papilio, Pterygota alata, Reevesia pubescens,Sterculia guttata and S. lanceifolia. Accessory vascular bundles are either collateral,amphivasal, or amphicribal in construction and even these bundles only with phloem tissueand completely devoid of any xylem element or vice versa, are also observed [e.g. distal partof petiole of Pterygota alata (Fig.2. C

3)]. Thus, these diverse features of the accessory

bundles as discussed above have huge taxonomic potential in the systematics of the membersof Sterculiaceae. Moreover, the sclerenchymatous fibre cells are often seen to embedwithin the phloem of the accessory bundles (Fig.1 & 2). Therefore, the characteristics ofaccessory vascular bundles play an important role towards the grouping of the studied taxaat species level. Of course, at generic level these characterizations do not afford any significantresult.

The petiolar vascular configurations as well as their number are exceptionally diversein the studies species. The number varies from single in Heritiera dubia (Fig.1. D

1-D

3) and

H. papilio (Fig.1. F1-F

3) to numerous in Pterygota alata (Fig.2. C

3) and Sterculia guttata

(Fig.2. F1). The number and arrangement also differ greatly at different topographic levels

of the petioles. Significantly these features do not show any generic relationship among thestudied members. However, they have a tremendous potential at species level identity. Theconfiguration at three different topographic regions of petiole (proximal, middle and distal) isso diverse that any species can be identified very easily at any growth stage.

It was suggested by Hare (1943) that the fewer number of vascular bundles in smallerleaves is perhaps due to their lesser need for water conduction, especially those under xericcondition. Later, this view was supported by Dehgan (1982). Present observation also agreeswith this hypothesis. Direct correlation has been observed between the length or diameter ofthe petiole, size of the lamina and number of vascular traces. Many to numerous bundles


Tabl

e – 2

. Com

para

tive

sta

tem

ents

of p

etio

lar

anat

omic

al fe

atur

es o

f 14

spec

ies

of S

terc

ulia

ceae



cont

inuo

us

have been observed in large-sized lamina with longer petiole (eg. Firmiana colorata,Sterculia foetida, Pterygota alata, etc.), however, one to few vascular bundles are seen insmall leaves with short petioles (eg. Melochia corchorifolia, Pentapetes phoenicea,Heritiera papilio, etc.).

Although secondary growth in the petiole is considered to be infrequent and also ofexciting finding (Dehgan 1982), all the studied species of Sterculia and Firmiana coloratashowed considerable secondary growth in their petioles. However, any ecological impactover this feature as advocated by Dehgan (1982) was not found as most of the studiedspecies were collected from more or less same tropical to subtropical climate and many ofthem exhibit equal periodicity of growth; even then only species of Sterculia and Firmianashow such type of unique developmental feature. This result proposes that the secondarygrowth in petiole show both developmental as well as ecology specific adaptability.

Vasculature of the petiole of species studied reveals great inter-specific variations whichare important in the grouping and delimitation of these species. Several authors advocated theimportance of combination of petiolar anatomical features in recognition of taxa, which couldbe of genuine overhaul to the taxonomists when used with proper indulgence and carefulness(Hare 1943; Howard 1962, 1979; Horn 2004; Shaheen 2006, 2007; Mandal 2010; Mitra &Maity 2013). Present investigation also provided sufficient evidence to prove the utility of thepetiolar anatomy of different members of Sterculiaceae towards the correct identity of species.An artificial key to the species is provided below using the petiolar anatomical characters.


Key to the species:1. Hypodermis collenchymatous ……… ……… ……… Firmiana colorata1. Hypodermis either absent or if present, parenchymatous …... 22. Vascular bundles numerous (more than 25) at proximal and

distal parts ………… ………… ……… ……… Pterygota alata2. Vascular bundles few, often 3 to 14 at proximal and distal

parts …..…… ………..… …..…… …………. 33. Vascular bundles numerous at middle part ……… ……… Sterculia foetida3. Vascular bundles few, often 1 to 6 at middle part ………… 44. Proximal part without any distinct pith; vascular bundles

aggregated at centre ……… ……… ……… …… 54. Proximal part with distinct pith; vascular bundles arranged in

more or less circular or semi-lunar fashion ……… …… 65. Pith at mid-petiole without mucilage cavity ……… …… Reevesia pubescens5. Pith at mid-petiole with mucilage cavity ……… ……… Sterculia lanceifolia6. Proximal part with accessory vascular bundles ………..… 76. Proximal part without accessory vascular bundles ……… 87. Accessory vascular bundle one throughout the petiole ….. Heritiera dubia7. Accessory vascular bundle more than one in major part of the

petiole (at least in any two zones) …… ……… …… 98. Accessory bundles united to a complex structure at mid-

petiole ……… ……… ……… ……… ……… Heritiera papilio8. Accessory bundles free from one another at mid-petiole ….. 109. Mucilage cavity one in pith region at proximal part ……….. Sterculia guttata9. Mucilage cavities more than one in pith region at proximal

part ……… ……… ……… ……… ……… Heritiera macrophylla10. Mid-petiole with a single circular vascular bundle ……….. 1110. Mid-petiole with few vascular bundles ……… ……….. 1211 Mid-petiole with accessory vascular bundles ……… ….. Helicteres hirsuta11. Mid-petiole without accessory vascular bundles ……….. Pterospermum

rubiginosum12. Vascular bundles horse-shoe-shaped at distal part ………… Eriolaena hookeriana12. Vascular bundles other than horse-shoe-shaped at distal part . 1313. Mucilage cavities absent in the pith at distal part ………… Melochia corchorifolia13. Mucilage cavities present in the pith at distal part ………… Pentapetes phoenicea

11 Mid-petiole with accessory vascular bundles ……… ….. Helicteres hirsuta11. Mid-petiole without accessory vascular bundles ……….. Pterospermum

rubiginosum12. Vascular bundles horse-shoe-shaped at distal part ………… Eriolaena hookeriana12. Vascular bundles other than horse-shoe-shaped at distal part . 1313. Mucilage cavities absent in the pith at distal part ………… Melochia corchorifolia13. Mucilage cavities present in the pith at distal part ………… Pentapetes phoenicea

Acknowledgements

Authors are thankful to the University Grants Commission, New Delhi, Govt. of India forfinancial assistance to carry out the research program. They are also thankful to Mr. KishoreBiswas, Research Scholar, Department of Botany, North Bengal University for his help inthe field to collect specimens. Prof. G. G. Maiti is warmly thanked for his advices andencouragement. Authors appreciate the corrections and suggestions of the referees, whocontributed to the improvement of this manuscript.

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