Notes on Discospermum sphaerocarpum Dalzell ex Hook.f., a rare species of Rubiaceae (Ixoroideae: Coffeeae) from southern India

: Discospermum sphaerocarpum is a rare species in the tribe Coffeeae of the family Rubiaceae and its occurrence on the Madayippara lateritic plateau of the Kannur district of Kerala, southern India is discussed. This plant is endemic to southern India and Sri Lanka. In Kerala, this species was previously recorded from the low-altitude evergreen forests of Thiruvananthapuram district. The present study gives a detailed description, distribution and figures & images illustrating the diagnostic characters of D. sphaerocarpum for easy identification and conservation.


INTRODUCTION
The genus Discospermum Dalzell ex Hook.f.comprises 13 species, mainly shrubs or trees, growing primarily in wet tropical biomes with native ranges from India to the Philippines (POWO 2023).In India, Discospermum is represented by three species, D. sphaerocarpum Dalzell ex Hook.f., D. apiocarpum Dalzell ex Hook.f., and D. abnorme (Korth.)S.J. Ali & Robbr.The former two species were reported in southern India and the latter one from Assam.D. sphaerocarpum is a medium-sized tree which grows in dry and wet tropical biomes and it is native to southern India and Sri Lanka (POWO 2023).
The genus was originally described by Dalzell in 1850 from Sri Lanka.Later, Hooker (1880) reduced the genus Discospermum to a section of Diplospora.This synonymy was widely accepted until Ali & Robbrecht (1991) revived Discospermum.To resolve the issue of the generic position of asian species classified as Tricalysia or Diplospora, Ali & Robbrecht (1991) reviewed traits of asian Diplospora/Tricalysia species, and proved that the Asian species cannot be accommodated within the African genus Tricalysia; and Discospermum, which was included in the synonymy of Diplospora for over a century, was reinstated at generic rank.They found that the two genera differ in placentation, fruit size and fruit wall texture, the number of seeds per locule, seed shape, and exotestal cell anatomy.Using molecular techniques, Arriola et al. (2018)  Another much-debated topic was the taxonomic placement of this genus.Initially, Discospermum was placed in the tribe Gardenieae.Robbrecht & Puff (1986) emended the circumscription of Gardenieae to include Tricalysia and Diplospora.Subsequently, Ali & Robbrecht (1991) attributed generic status to Discospermum, and included it in the Gardenieae subtribe Diplosporinae.They stated that Discospermum "links the Diplosporinae with the Gardeniinae and supports the rank (subtribe) given to these".Results of the phylogenetic study by Andreasen & Bremer (2000) do not support such a relationship and they concluded that at least some genera of Diplosporinae belong to Coffeeae.In a recent study, Davis et al. (2007) expanded the circumscription of Coffeeae and confirmed the placement of Discospermum in this tribe based on plastid sequence data and morphological data set.
Previous reports of the species Discospermum sphaerocarpum in India were from the wet and dry evergreen forests from the coast to high altitudes (50-1,000 m) of the Western Ghats regions of Kerala, Tamil Nadu, Karnataka, Goa, and Maharashtra (Singh et al. 2015).Gamble (1921) reported the species from Courtallum of Tinnevelly (Tirunelveli) district of Tamil Nadu; later distribution record extended to Cuddalore and Villupuram districts and Coromandel coast (Narayanasami & Natesan 2020).In Kerala, D. sphaerocarpum was earlier reported from the lowelevation evergreen forests of Thiruvananthapuram district (Sasidharan 2004).This species now has been recorded from a totally different habitat close to seashore, the sacred groves of a Lateritic hill of Madayippara at an altitude of less than 50 m in the Kannur district (Pramod & Pradeep 2020, 2021).
During a botanical exploration of the Madayippara lateritic plateau of southern India in 2008, the authors encountered a rare Rubiaceae member in vegetative condition in two patches of vegetation associated with sacred groves.The identity of the species remained a mystery as no flowering was seen in the two populations until early January 2014, when the plant produced a few flower buds which did not open.However, after a gap of five months, following the first summer shower in May, the flowers opened.After critical studies of the specimens, they were referred to Dr. S.E.Dawson, Rubiaceae systematics, Herbarium Royal Botanic Gardens, Kew, and confirmed the identity as Discospermum sphaerocarpum, and commented "it is very interesting that it comes from such a different habitat" (Sally Dawson pers. comm. 13.vi.2014).The aforementioned pattern of flowering was repeated in the year 2023 as well.The present paper aims to provide a detailed taxonomy, distribution and conservation status, illustration and photographic images of D. sphaerocarpum, for future reference and conservation.

MATERIALS AND METHODS
The present account of the species Discospermum sphaerocarpum is based on two populations; one growing in a sacred grove associated with Madayikkavu Thiruvarkkattu Bhagavathi temple and another one in an undisturbed patch of vegetation in a private land near Sree Chalilkkavu Bhagavathi temple (Image 1A,B).The current location is in the northernmost of Kerala, in Madayippara lateritic plateau in the Kannur district, which has a completely different habitat not far separated from the sea coast.Madayippara is one of Plant materials were collected from the two populations available at Madayippara lateritic plateau for laboratory studies and preparation of voucher specimens.The specimens collected for laboratory studies were worked out using LEICA M80, ZEISS Stemi DV4 and LABOMED CSM2 microscopes.Photographs of the plant specimens and habitats were taken using Nikon Coolpix L110 and Olympus C-7070 cameras.The voucher specimens were prepared following wet method (Fosberg & Sachet 1965) and are deposited at the Calicut University Herbarium (CALI).The distribution status was determined from 'Plants of the World Online' (POWO), pertinent floras and literature; and the distribution map was created using QGIS ver.3.28.2(QGIS 2022).
Phenology: Since 2008, flowering in this species was observed only twice, in the year 2014 and 2023.The buds appeared in early January, and remained dormant till the middle of May (until heavy summer shower), and the fruits were seen till July.

Image 1 .
Economic importance: The berries are known as wild coffee; the drink made from the roasted and powdered seeds has a coffee flavour.In addition to 24424 Discospermum sphaerocarpum Dalzell ex Hook.f.: A-B-habitats of populations | C-leafy twig | D-domatia on the abaxial surface of leaf | E-stipule | F-bole | G-twig with flower buds | H-flower buds on a node | I-developing buds | J-flowers | K-mature fruits.© A,B,C,F-K-Pramod C.; D-E-Drisya V.V.