Bruguiera cylindrica

Bruguiera cylindrica View in CoL : INDIA, Kerala, Ernakulam district, mangroves near high intertidal edge of Vembanad lake , N 10.00°, E 76.22°, 27.03.2019, Prasanna Rajan 11020 ( CATH) GoogleMaps .

Bruguiera gymnorhiza : INDIA, Kerala, Alappuzha district, Sreekantamangalam vicinity, near high intertidal edge of Vembanad lake, N 9.66°, E 76.36°, 21.03.2019, Prasanna Rajan 11015 (CATH); Ernakulam district, mangroves near high intertidal edge of Vembanad lake, N 10.00°, E 76.22°, 27.03.2019, Prasanna Rajan 11017 (CATH); Kottayam district, Thalayazham vicinity, mangroves nearhigh intertidal edge of Vembanad lake, N 9.69°, E 76.41°, 18.03.2019, Prasanna Rajan 11010 (CATH); T.V. Puram vicinity, mangroves near high intertidal edge of Vembanad lake, N 9.70°, E 76.39°, 18.03.2019, Praanna Rajan 11011 (CATH).

Bruguiera sexangula : INDIA, Kerala, Alappuzha district, Sreekantamangalam vicinity, near high intertidal edge of Vembanad lake, N 9.66°, E 76.36°, 21.03.2019, Prasanna Rajan 11016 (CATH); Ernakulam district, mangroves near high intertidal edge of Vembanad lake, N 10.00°, E 76.22°, 27.03.2019, Prasanna Rajan 11018 (CATH); Kottayam district, Thalayazham vicinity, mangroves near high intertidal edge of Vembanad lake, N 9.69°, E 76.41°, 18.03.2019, Prasanna Rajan 11009 (CATH); T.V.

Puram vicinity, mangroves near high intertidal edge of Vembanad lake, N 9.70°, E 76.39°, 18.03.2019, Prasanna Rajan 11012 (CATH). Key to Bruguiera taxa in mainland India genetic traits, comparing populations across their

1. Flowers in inflorescence, always less than 2 cm global range.

in length; hypocotyl widest diameter less than In eastern populations of B. sexangula , there

1 cm .................................................................. 2 were comparatively short bristles reported on

1. Flowers solitary, always greater than 3 cm petal lobes ( Duke & Ge, 2011) matching those in

in length; hypocotyl widest diameter greater Indian populations. In addition, B. sexangula had

than 1 cm ........................................................ 3 hairs fringing petal margins, petal bristles were

2. Calyces with reflexed lobes reflexed in fruit ...... absent or singular if present, with lengths less than

.......................................................... B. cylindrica 1 mm or minute, petal lobe tips obtuse, and calyx

2. Calyces with completely adpressed lobes in lobes slightly reflexed on mature hypocotyls.

mature hypocotyls ........................ B. parviflora In Indian sites, B. gymnorhiza had acute petal lobe

3. Petals with margins fringed with hairs, lobe tips, petals with two or three bristles greater than

apices glabrous or if bristles present, equal to 2 mm long, with margins mostly glabrous or

or less than 1 mm in length ........... B. sexangula sparsely hairy. To the east, the petal margin

3.

Petals with margins without fringed hairs, lobe character was reported as variable often with

apices with 1–3 bristles, greater than 1 mm in fringing hairs ( Sheue et al., 2005; Duke & Ge, 2011; Ragavan et al., 2016). These observations identified

length .............................................................. 4

an apparent difference in diagnostic characters

4. Petals with 2–3 bristles, greater than 2 mm in between regions. But, as shown in the MDS

length .......................................... B. gymnorhiza plot ( Fig. 1b View Fig ), there appeared to be only

4. Petals with 1–2 bristles, less than 2 mm in minor variation in overall characters where B. ×

length ..................................... B. × rhynchopetala rhynchopetala specimens were positioned more or less equidistant between B.

sexangula and B. gymnorhiza (similar to that

DiScuSSion shown by Duke & Ge, 2011). Based on

Of primary note, B. × rhynchopetala reported in current evidence, we conclude that the intermediate

the present study was not fully consistent with taxon is most likely to be the hybrid B. ×

descriptions of this taxon from the western rhynchopetala , positioned between its putative

Pacific ( Sheue et al., 2005, Duke & Ge, 2011;). parent species, B. sexangula and B. gymnorhiza .

Differences were observed in various characters Although, as noted, the later taxon had distinct

notably with regard to the petal margins morphological differences from populations in the

being mostly glabrous in Indian material instead east.

of having fringing hairs along the margins. In We are aware of other potentially diagnostic

addition, petals in Indian specimens had two characters, like the colleters at the base of the

unequal bristles instead of 2–3 bristles, while the conspicuous interpetiolar stipules of this genus

calyces were ribbed instead of being variable. ( Hou, 1958; Sheue et al., 2013). However, for

While these differences were notable, they were this assessment, we have relied on morphological

not considered sufficient for further specific characters known to be diagnostic for comparable

differentiation based on current collections at this taxa within this genus worldwide (Duke & Ge,

newly established western limit. It was further 2011; Cooper et al., 2016; Duke & Kudo, 2018).

relevant that the intermediate taxon, B. ×

rhynchopetala was located in close proximity to In summary, B. × rhynchopetala differs from

both B. gymnorhiza and B. sexangula . Additional B. sexangula but is similar to B. gymnorhiza

studies could contribute to further elucidating the in not having fringed hairs at the petal lobe

morphological differences amongst Indian margin, similar length of the petal lobe and

collections of B. gymnorhiza a nd B. sexangula , petal lobe tip shape. While the hybrid is similar to B.

as well as presenting an evaluation of possible sexangula but differs from B. gymnorhiza in having ribbed calyx tubes, fewer calyx lobes that are slightly reflexed in mature hypocotyls.

Reports until now revealed the existence of a hybrid intermediate only in countries in the eastern portion of the parental overlap zone in both northern and southern hemispheres like southern China, Malesia, Papua New Guinea and northern Australia ( Duke & Ge, 2011; Muhamad et al., 2016; Tomlinson, 2016; Duke, 2017). This observation led to a working view that B. gymnorhiza and B. sexangula populations in the west (southern India and Sri Lanka) may have greater genetic separation, as an explanation for the apparent lack of hybrids in the western part of the range ( Sheue et al., 2005; Duke & Ge, 2011). With this new observation of a distant population of B. × rhynchopetala beyond its known south-eastern Asian, eastern Asian and western Pacific distribution ( Fig. 3 View Fig ), we raise important questions about the description and identification of Bruguiera taxa throughout the region. Such questions warrant further investigations across the region to develop a clearer understanding of morphological and genetic differences between eastern and western populations.

The distribution of B. sexangula appears limited further to comparatively lower salinity backwater zones, while B. gymnorhiza occurs naturally in a their possible niche separation ( Duke, 2006). The hybrid was observed mostly in back water zones where B. sexangula was more abundant than B. gymnorhiza (also consider Zhou et al., 2008).

In addition, as well as being of great biogeographical and socio-economic significance, the Vembanad wetland ecosystem is facing notable threats from environmental degradation ( Asha et al., 2014). The mangrove forests of Kerala are now only a remnant of their past extent ( Mini et al., 2014). During the last three decades, the Kerala coast has lost a significant proportion of its mangrove forests ( Sreelekshmi et al., 2020), the destruction is much higher in the Ernakulam district with remaining mangrove and natural estuarine areas located mostly around the Vembanad lake ( Rani et al., 2018; Sreelekshmi et al., 2020). During the period between 1973 and

2015, there were losses of 6.93% (~ 12.28 km ²)

( Parvathy & Babu, 2016). Accordingly, our current observations not only update the distribution status of B. × rhynchopetala , but they also emphasise the great need for urgent conservation of these valued but threatened ecosystems of south-western India.