THAI FOREST BULL., BOT. 45(1): 58–78. 2017. DOI: 10.20531/TFB.2017.45.1.10 Stories from the Mekong, part 2. The Cryptocoryne (Araceae) of Chiang Khan District, Loei Province, Thailand TAKASHIGE IDEI1,*, JAN D. BASTMEIJER2 & NIELS JACOBSEN3 ABSTRACT Between March 2006 and February 2015, the occurrence and habitats of the aroid genus Cryptocoryne were investigated in Chiang Khan District, Loei Province, Thailand. In addition to the well-known Cryptocoryne crispatula Engl. var. crispatula and C. crispatula var. yunnanensis (H.Li) H.Li & N.Jacobsen, a recently described species was found: C. loeiensis Bastmeijer et al., as well as a number of plants considered to be hybrids. Although Cryptocoryne is presently abundant, decimation or extinction could occur in the future because of the dam constructions in the Mekong River. KEYWORDS: Cryptocoryne, Araceae, habitats, hybrids, floodplain, hydro-power dam. Published online: 26 September 2017 INTRODUCTION mentioned in this article may be found in Jacobsen (1980), Bastmeijer (2017) and in Jacobsen et al. The Mekong River (Mae Nam Khong) is the (2012) regarding their occurrence in Thailand. longest river in Southeast Asia, running through six countries with a length of around 4,800 km and Maxwell (2009), presented a survey of the emptying into the South China Sea. Its catchments vegetation and flora of the Mekong between Kratie area is about 795,000 km2, approximately about 1½ and Stung Treng, in central Cambodia, where times as large as Thailand or France. The biodiversity Cryptocoryne crispatula var. crispatula was recorded. of the Mekong River basin is only exceeded by that Puff & Chayamarit (2011) presented a study of the of the Amazon River basin, and it is one of the most rheophytes of the Mekong at the Pha Taem N.P., productive inland fisheries in the world, with over some 800 km further down the Mekong from Chiang 1300 fish species (WWF, 2008). The present study Khan together with data from the Mekong River area Chiang Khan is located about 1,700 km from basin, but did not report any Cryptocoryne. the estuary, at an altitude of about 200 m a.s.l. Observations were made during March–April 2006, CLIMATE March 2007, March 2008, January 2010, August 2010, January 2011, and February 2015. Chiang Khan has a tropical savanna climate with an average annual temperature of about 26°C. The first part of ’Stories from the Mekong’, The dry season is from November to April with an was published by Idei et al. (2010) with the description average monthly precipitation of around 16 mm, and of two new taxa of Cryptocoryne: C. mekongensis the driest period (December and January) having Idei et al. and C. crispatula var. decus-mekongensis total average rainfall of merely 8 mm. The rainy Idei et al., with pictures of their habitats in southern season is from May until September with an average Lao P.D.R. as well as of the plants. An overview of precipitation of around 1100 mm per month (Climate- the genus Cryptocoryne as well as other species data, 2017). 1 23–14, 1 Chome Amanogahara, Katano City, Osaka 576-0034, Japan. 2 Oude Roswinkelerweg 72, NL 7822 AG Emmen, The Netherlands. 3 Section of Organismal Biology, Department of Plant- and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark. * Corresponding author: [email protected] © 2017 The Forest Herbarium STORIES FROM THE MEKONG, PART 2. THE CRYPTOCORYNE (ARACEAE) OF CHIANG KHAN DISTRICT, LOEI PROVINCE, THAILAND (T. IDEI, J.D. BASTMEIJER & N. JACOBSEN) 59 There is a period of relative low temperatures sedimentary rocks, such as mud rock with the slaking, from December to February with a daily mean low slate, clastic dike, granule-cobble conglomerate, and of 15°C (frequently down to 9°C), and a daily mean convolute bedding, are seen frequently. Heaps of high of 29°C (up to 34°C). A higher temperature exposed large boulders, and high rocky shelves that period from March and April has a daily high of are found elsewhere in the Mekong flood plain do 34°C (frequently rising to 41°C), and a daily low of not occur in the investigated area. 22°C (occasionally as low as 19°C). The daily tem- perature range from May to September is narrower RIVER PROFILE with a daily low of around 23°C (for a month mean) to daily high of around 32°C (Accuweather, 2017; Water level: Figure 3A shows the annual water Climate-data, 2017; Tempstat, 2017). level fluctuation for selected years. The absolute water depth, is based on a zero gauge of 194 m above The rainfall in the upper parts of the Mekong MSL by an official water gauge in Chiang Khan. catchments region influences the water level fluctua- The minimum water level is defined as 1.9 m, and tions more than does the local rainfall, and thus has floodwater level is defined as 17.4 m (Mekong River an influence on the Cryptocoryne ecology in the Commission, 2017; for additional data see also Puff shallow water places during the dry season. In the & Chayamarit, 2011). Figure 3B–C shows the water smaller tributaries to the Mekong the local rainfall level measurement scale at Chiang Khan on 1 January is of more importance as regards the situation in the 2010. local habitat. The water level fluctuation at Chiang Khan originates from the rainfall in the upriver districts INVESTIGATION AREA (especially in northern part of the Lao P.D.R.) rather The study site is on sedimentary rock in the than the local weather, and a temporary rise in water meandering riverbed about 35 km downstream from level occurs frequently even during the dry season. Chiang Khan, focused on the five areas of Chiang Furthermore, the actual water level is always fluc- Khan western part, Chiang Khan eastern part, Kaeng tuating owing to ripples or small waves, and these Khut Khu (Kaeng Kood Koo), Ban Pah Baen and are not reflected in daily water gauge data. When Ban Hat Bia; all with abundant Cryptocoryne standing on the river bank one can frequently see populations. The width of the river varies from about fluctuations of more than 15 cm within a minute and 0.3 km to 1.2 km, and at Chiang Khan town, it is this is especially notable at water levels below 4.0 approximately 0.6 km wide. The open laterite soil m. Hydropower dams operating in the upstream of in the steep riverbanks (Fig. 1A) and the boundary China’s Yunnan Province have continuously been of the secondary forests clearly reveals the extent affecting water level fluctuations in recent years. of the highest water levels (Fig. 1B), where the soft During the rainy season the muddy water soils are often collapsing owing to river erosion contains soil particles and various types of driftwood during high water, and also owing to the deforestation and other floatingfragments . Water visibility is always along and around the riverbanks. The three segments the less than 10 cm in August. The clearest water in the river profile are the steeply inclined riverbank, flow is found from the middle of March to the the seasonal floodplain, which is to some extent beginning of April, with visibility increasing to a undulated, and the channel of the perennial river. depth of about 80 cm in the clearest parts. The seasonal The channel of the perennial river is not braided surface water temperature in the mainstream varies between Chiang Khan and Pak Chom. The floodplain from January (ca 22°C) to March–April (ca 29°C). may amount to about 60–90% of the width of the river in the latter half of the dry season, when it has a prominent detritus cover. Local residents perform FLOODPLAIN seasonal agriculture on the exposed floodplain during The floodplain is generally below the water the dry season (Fig. 2). The sedimentary rock riverbed level at 6.5 m (see Fig. 3). The soil surface emerges is overall comparatively flat, although moderately gradually after the middle of November with numerous steep places do occur. Characteristics of various ephemeral shallow rapid streams occurring on the 60 THAI FOREST BULLETIN (BOTANY) VOL. 45 NO. 1 Figure 1. Seasonal water level fluctuation in front of Chiang Khan town; A. 5 April 2006, with a water level of ca 3.5 m. The bare laterite soil of the steep riverbank and the boundary of the secondary forests shows the extent of the highest water levels; B. 15 August 2010, water level ca 10.5 m. Photographs by T. Idei unless otherwise stated. STORIES FROM THE MEKONG, PART 2. THE CRYPTOCORYNE (ARACEAE) OF CHIANG KHAN DISTRICT, LOEI PROVINCE, THAILAND (T. IDEI, J.D. BASTMEIJER & N. JACOBSEN) 61 Figure 2. Seasonal agriculture on the high accumulated mobile sand at Ban Pah Baen during the dry season, 13 January 2010. The accumulated layer consists of mobile detritus; the vertical accumulation range varies from the thin layer immediate above the sedimentary rock to more than 5 m in sheltered places. floodplain. Creeks and stagnant pools are then formed section is inhabited by the aquatics Hydrilla in openings on the sedimentary rock that emerges verticillata (L.f.) Royle, Najas indica (Willd.) during the latter half of the dry season (Fig. 4A). Cham., Potamogeton crispus L., and Vallisneria The floodplain consists of a sediment layer gigantea Graebn. As the eastern part of Chiang and a surface accumulation layer (Fig. 4B). The Khan, located about 1 km downstream from the sediment layer is composed of an assortment of water gauge, an amphibious vegetation layer is deposited detritus with stones of various sizes due to situated immediately above the aquatic layer in the the undertow.