The family Rubiaceae in southern Assam with special reference to endemic and rediscovered plant taxa

Acknowledgements: The first author is grateful to P. Singh, Director, Botanical Survey of India (BSI), Kolkata and to A.A. Mao, Scientist-E and Head of Office, BSI, Eastern Regional Centre, Shillong for facilities and encouragement. The authors also extends their sincere thanks to Board of Trustees of the Royal Botanic Gardens, Kew for providing the digital images of type specimens. The family Rubiaceae is widespread and occurs in all major regions of the world except Antarctica and shows maximum proliferation in low to mid altitude humid forests. The family comprises 13,143 species falling under 611 genera by which it is the fourth largest Angiosperm family (Davis et al. 2009). In India, it is represented by 551 species of which 67% taxa (365 spp.) are endemic (Sambamurthy 2005). Kar & Panigrahi (1963) reported 118 species from Assam and the North East Frontier Agency (present Arunachal Pradesh), whilst Chowdhury (2005) listed ca. 150 species of Rubiaceae from the state of Assam. Southern Assam (Barak Valley) is located between 24008’–25008’N and 92012’–93015’E. The valley covers an area of 6,922km2 and is surrounded by Dima Hasao District and Jaintia Hill in the north, the Manipur Hills in the east and the Mizoram Hills in the south. To the west the plains merge with the Sylhet plains of Bangladesh and the Indian state of Tripura. At present the region is divided into three administrative districts Cachar, Karimganj and Hailakandi. The 2,339km2 forest area comprises of 12 reserve forests and one wildlife sanctuary, i.e., ca. 34% of the total geographical area of the valley. The drainage system of southern Assam is fed by 18 major rivers and rivulets and Barak is the chief river which flows in an eastwest direction through the central part of the valley. The annual average rainfall and temperature ranges from 2500–4000 mm and 7.5–40 0C, respectively; whereas, the relative humidity varies from 60–91 %. The vegetation of the region predominantly consists of tropical wet evergreen to tropical semi-evergreen forest types (Champion & Seth 1968). Tropical wet evergreen type of forest is prevalent in the northern and eastern slopes of southern Assam like Borail Hill Ranges, Lower Jiri Reserve Forest, Barak RF, and Inner Line RF. The dominant tree species of this type of forest are Actinodaphne Abstract: Analysis of diversity, distribution and endemism of the family Rubiaceae for southern Assam has been made. The analyses are based on field observations in the three districts, viz., Cachar, Hailakandi and Karimganj, as well as data from existing collections and literature. The present study records 90 taxa recorded from southern Assam, four of which are endemic. Chassalia curviflora (Wall.) Thwaites var. ellipsoides Hook. f. and Mussaenda keenanii Hook.f. are rediscovered after a gap of 140 years. Mussaenda corymbosa Roxb. is reported for the first time from northeastern India, while Chassalia staintonii (H.Hara) Deb & Mondal is reported as a new record for Assam.

The family Rubiaceae is widespread and occurs in all major regions of the world except Antarctica and shows maximum proliferation in low to mid altitude humid forests.The family comprises 13,143 species falling under 611 genera by which it is the fourth largest Angiosperm family (Davis et al. 2009).In India, it is represented by 551 species of which 67% taxa (365 spp.) are endemic (Sambamurthy 2005).Kar & Panigrahi (1963) reported 118 species from Assam and the North East Frontier Agency (present Arunachal Pradesh), whilst Chowdhury (2005) listed ca.150 species of Rubiaceae from the state of Assam.
Southern Assam (Barak Valley) is located between 24 0 08'-25 0 08'N and 92 0 12'-93 0 15'E.The valley covers an area of 6,922km 2 and is surrounded by Dima Hasao District and Jaintia Hill in the north, the Manipur Hills in the east and the Mizoram Hills in the south.To the west the plains merge with the Sylhet plains of Bangladesh and the Indian state of Tripura.At present the region is divided into three administrative districts Cachar, Karimganj and Hailakandi.The 2,339km 2 forest area comprises of 12 reserve forests and one wildlife sanctuary, i.e., ca.34% of the total geographical area of the valley.The drainage system of southern Assam is fed by 18 major rivers and rivulets and Barak is the chief river which flows in an eastwest direction through the central part of the valley.The annual average rainfall and temperature ranges from 2500-4000 mm and 7.5-40 0 C, respectively; whereas, the relative humidity varies from 60-91 %.
The vegetation of the region predominantly consists of tropical wet evergreen to tropical semi-evergreen forest types (Champion & Seth 1968).Tropical wet evergreen type of forest is prevalent in the northern and eastern slopes of southern Assam like Borail Hill Ranges, Lower Jiri Reserve Forest, Barak RF, and Inner Line RF.The dominant tree species of this type of forest are Actinodaphne

Materials and Methods
Field surveys were conducted from 2010 to 2013 in 2,339km 2 forest area, to assess the diversity, distribution, endemism and threats to the family Rubiaceae in different parts of southern Assam, particularly in reserve forests and wildlife sanctuaries.This was supplemented with a literature study of peer-reviewed papers, monographs and floras, followed by a study of the herbarium specimens housed at Botanical Survey of India, Eastern Regional Centre, Shillong (ASSAM).Digital images of type specimens were obtained from the Royal Botanical Gardens, Kew (UK) to confirm the identity of the species.Species distributions were plotted using Google Earth v. 6.1.0.5001 (www.earth.google.com).Extent of Occurrence (EOO) were calculated by drawing a minimum convex polygon and areas were worked out by using the software GE Path v. 1.4.6 (Sgrillo 2012).Similarly Area of Occupancy (AOO) was calculated by the sum of the occupied isometric grid squares of size 20km 2 (Image 1B).
The regional taxa of southern Assam were then subjected to two step assessment procedure: In step one, criteria B & D (IUCN 2001), were applied to the selected regional population of the selected taxon, resulting in a preliminary categorization.In step two, the existence and status of any conspecific populations outside the region that may affect the risk of extinction within the region was investigated either through field visit or based on information from herbarium data and published regional floras.If the taxon was found endemic to the region, the Red List category defined by the criteria was adopted unaltered and if on the other hand, conspecific populations outside the region were judged to experience a "rescue effect" to the target population, the global assessment was downgraded by one step to fit the IUCN regional Red List guidelines (IUCN 2003), such as changing the category from Endangered (EN) to Vulnerable (VU) or from VU to Near Threatened (NT).Taxa that have been upor downgraded in the regional Red List is clearly indicated by a dot after the category.
Taxa falling under the IUCN Red List Criteria are dealt in detail with -synonyms if any, description, phenology, distribution and specimen(s) examined as well as their status, and criteria for determining the status.Materials cited in Table 1 have been seen and are deposited in the herbarium of Botanical Survey of India, Eastern Regional Centre (ASSAM), unless otherwise stated.Digitalized specimens are cited along with their barcodes.

Results and Discussion
A total of 90 taxa are recorded in the present study (Table 1), of which genera Ixora, Ophiorrhiza and Psychotria have a maximum number with seven taxa each, followed by Oldenlandia with six taxa, Mussaenda with five taxa, Chassalia and Lasianthus with four taxa each, Tarenna and Uncaria are represented by three taxa each and Cephalanthus, Leptomischus, Mitragyna,   Enumeration of threatened and endemic taxa 1. Acranthera tomentosa Hook.f., Fl.Brit.India 3: 92.1880; Kanjilal et al., Fl. Assam 3: 48. 1939.
Global Red List Category: Not Evaluated.
Regional Red List Category and Criteria: The taxon was known only from its type collection and the present collection is made after 140 years.Extent of occurrence is estimated to be ca.40km 2 (Criteria EN B1<5,000km 2 ); The area of occupancy is calculated to be ca.20km 2 (Criteria EN B2<500km 2 ), while there is a continuous decline in area of occupancy due to slash-and-burn cultivation and tree felling (Criteria EN B2b(ii)).Following IUCN Red List Categories and Criteria (IUCN 2001), this taxon has been classified as Endangered (EN).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.
Note: This taxon was first described by Hooker (1880) on the basis of a collection made by C.B. Clarke in 1872 from Jarain area in Jaintia Hills of Meghalaya.Thereafter this variety was not reported to be collected by anyone.Hence, the present collection made after 140 years is a new record for the state of Assam.Global Red List Category: Not Evaluated.Regional Red List Category and Criteria: The area of occupancy is ca.505km 2 (Criteria VU B2<2,000 km 2 ), currently known from about six locations (Criteria VU B2˂10), while there is a continuous decline in area of occupancy due to slash-and-burn cultivation and tree felling (Criteria VU B2b(ii)).Following IUCN Red List Categories and Criteria (IUCN 2001), this taxon has been classified as Vulnerable (VU).As there is are possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.
Global Red List Category: Vulnerable (IUCN 2012).Regional Red List Category and Criteria: The Extent of occurrence is estimated to be ca.25km 2 (Criteria EN B1<5,000km 2 ).The area of occupancy is calculated to be ca.11km 2 (Criteria EN B2<500 km 2 ) and there is only one known locality (Criteria EN B1a≤5), while there is a continuous decline in area of occupancy due to encroachment of National Highway 54 (Criteria EN B2b(ii)).
Following IUCN Red List Categories and Criteria (IUCN 2001), the species has been classified as Endangered (EN).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.Global Red List Category: Not Evaluated.

Ixora rangonensis
Regional Red List Category and Criteria: The Extent of occurrence is estimated to be ca.15km 2 (Criteria CR B1<100km 2 ); The area of occupancy is estimated to be 8km 2 (Criteria CR B2˂10km 2 ), known to exist at only a single location (Criteria CR B2a).The population size is estimated to number less than 10 individuals and so far only one plant was seen (Criteria CR D˂50 mature individual), while there is degradation of the habitat (Criteria CR B2b(iii)) due to slash-and-burn cultivation and tree felling.Following the IUCN Red List Categories and Criteria (IUCN 2001), this species has been classified as Critically Endangered (CR).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.

A B C
glabrous, throat with a ring of stiff hairs.Stamens 5. Ovary 2-loculed, ovules 8.; style short; stigmas 2, flat.Fruits not seen.Flowering: April.Distribution: India [Assam (Cachar)], Endemic.Specimen examined: Nil.Global Red List Category: Not Evaluated.Regional Red List Category and Criteria: The species is presumed to be Extinct (EX) because an exhaustive survey in the type locality by D.B. Deb in October 1995 (Deb 2001) and by the authors from 2010-2013 to relocate the plant in its type locality or anywhere in the Barak valley region proved futile.The type specimens were collected before the establishment of tea gardens, which might have been the cause of its extinction.
Regional Red List Category and Criteria: The Extent of occurrence is estimated to be ca.35km 2 (Criteria EN B1<5,000km 2 ); The area of occupancy is calculated to be ca.15km 2 (Criteria EN B2<500km 2 ), known to exist from two locations (Criteria EN B2a≤5), the area of occupancy is rapidly decreasing due to slash-and-burn cultivation (Criteria EN B2b(ii)).Following IUCN Red List Categories and Criteria (IUCN 2001), the species has been classified as Endangered (EN).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.

D E F
Balakrishnan collected the plant from Sohha-Dawki area of Meghalaya.
Global Red List Category: Not Evaluated Regional Red List Category and Criteria: The extent of occurrence is calculated to be ca.50km 2 (Criteria CR B1<100km 2 ); area of occupancy is estimated to be ca.2.2km 2 (Criteria CR B2<10km 2 ), currently known to exist from a single location (Criteria CR B2a) and the area of occupancy is decreased due to the establishment of Gopal Tilla T.E., Kalain, Cachar, Assam (Criteria CR B2b(ii)).Following the IUCN Red List Categories and Criteria (IUCN 2001), this species has been classified as Critically Endangered (CR).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.
Regional Red List Category and Criteria: The area of occupancy is calculated to be ca.502km 2 (Criteria VU B2<2,000km 2 ), currently known to exist in 5-6 locations (Criteria VU B2a≤10).The area of occupancy is rapidly decreasing due to slash-and-burn cultivation (Criteria B2b(ii)).Following the IUCN Red List Categories and Criteria (IUCN 2001), this species has been classified as Vulnerable (VU).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.
Specimens examined: 73181 (ASSAM), 10.ix.1978,Assam, Cachar, Amraghat, coll.R.B. Majumdar; 914 (ASSAM), 03.vi.2012, Bhuban Hill, coll. H.A. Barbhuiya.Global Red List Category: Not Evaluated Regional Red List Category and Criteria: The area of occupancy is estimated to be ca.503km 2 (Criteria VU B2<2,000 km 2 ), currently known to exist in six locations (Criteria VU B2b≤10); there is a continuous decline in area, extent and quality of habitat due to encroachment of forest land (Criteria VU B2b(iii)).According to IUCN Red List Categories and Criteria (IUCN 2001), it meets the criteria for Vulnerable (VU), but due to rescue possibilities from adjacent regions, it is downgraded by one step to Near Threatened (NT) regionally.Hook. f., Fl. Brit. India 3: 174. 1880;Deb & M. Gangop. in J. Econ. Taxon. Bot., Addit. Ser. 7: 144. 1989 Global Red List Category: Not Evaluated Regional Red List Category and Criteria: Area of occupancy estimated to be ca.501km 2 (Criteria VU B2<2,000km 2 ), currently known to exist in 6 locations (Criteria VU B2a≤10); the quality of habitat is rapidly decreasing due to slash-and-burn cultivation and encroachment of forest land (Criteria VU B2b(iii)).Following the IUCN Red List Categories and Criteria (IUCN 2001), this species has been classified as Vulnerable (VU).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.
Specimen examined: 4724 (ASSAM), 18.xi.1914,Assam, Cachar, Phulertal, coll.U.N. Kanjilal;112233 (ASSAM), 17.viii.2013, Lower Jiri Reserve Forest, coll. H.A. Barbhuiya.Global Red List Category: Not Evaluated Regional Red List Category and Criteria: The Extent of occurrence is estimated to be ca.101km 2 (Criteria EN B1<5,000km 2 ); Currently known from about three locations (Criteria ENB2a<5).The area of occupancy is estimated to be ca.60km 2 (Criteria EN B2<500 km 2 ); there is a continuous decline in area, extent and quality of habitat due to encroachment of forest land (Criteria EN B2b(iii)).Following IUCN Red List Categories and Criteria (IUCN 2001), it has been categorized as Endangered (EN).As there is no possibilities of rescue from neighboring regions, hence there is no change to the initial assessment.

Conclusions
The Rubiaceae members are ecologically sensitive and in combination with other factors such as restricted distribution, they are vulnerable to extinction (Davis et al. 2009).With the increase in human population, expansion of agricultural ac tivities, over-exploitation of forests for firewood, shifting cultivation, extensive timbering, construction of roads and other developmental activities, the forest cover of the region is rapidly shrinking and as a result the threatened taxa of the region become more endangered.At present southern Assam has 116 tea gardens covering 8.14% of the total geographical area of the region.Tropical rainforests were massively destroyed for the establishment of tea gardens from 1858-1937.It is obvious that herbaceous plants discovered prior or during that period had nearly disappeared, particularly those which had a limited population or were too restricted in distribution.
The present study has allowed us to identify 14 threatened taxa, of which two are already extinct from the region while the remaining are to be conserved as top priority.Efforts should be made to protect and preserve the particular localities and habitats of these plants.The germplasm of all the surviving threatened taxa should be conserved in botanic gardens as ex situ conservation.It is suggested that these plants be multiplied through tissue culture techniques and reintroduce the propagated clones to their natural habitats.
Image 1.A -Map of India showing location of southern Assam.B -Grid map of southern Assam.
Notes: Leptomischus wallichii (Hook.f.) H.S. Lo was established by Hooker in 1873 as Polysolenia wallichii on the basis of a collection made by W. Gomez from Khasia Mountains , in the mean time R.L. Keenan also collected the plant from Cachar District of Assam.Later in 1968, Image 2. D -Ixora rangonensis Bremek.; E -Mussaenda corymbosa Roxb.; F -Mussaenda keenanii Hook.f.

Table 1 . List of Rubiaceae members recorded from southern Assam 5652
Mussaenda keenanii Hook.f. and Leptomischus wallichii (Hook.f.) H.S. Lo are restricted to Assam and Meghalaya only.Mussaenda corymbosa Roxb. is reported for the first time from northeastern India and Chassalia curviflora (Wall.)Thwaites var.ellipsoides Hook.f. and Chassalia staintonii (H.Hara) Deb & Mondal are reported for the first time from Assam based on our collections.Chassalia curviflora var.ellipsoides and Mussaenda keenanii are rediscovered after a gap of ca.140 years; present collections of both the taxa also constitute their second authentic collection after type.