A taxonomic revision of Rhizophora L. (Rhizophoraceae) in Thailand.

A taxonomic revision of Rhizophora L. (Rhizophoraceae) in Thailand is presented. Two species, R. apiculata Blume and R. mucronata Poir., are enumerated with updated morphological descriptions, illustrations and a taxonomic identification key, together with notes on distributions, habitats and ecology, phenology, conservation assessments, etymology, vernacular names, uses, and specimens examined. Three names in Rhizophora, are lectotypified: R. apiculata and two associated synonyms of R. mucronata (i.e., R. latifolia Miq. and R. macrorrhiza Griff.). R. longissima Blanco, a synonym of R. mucronata, is neotypified. All two Rhizophora species have a conservation assessment of Least Concern (LC). Based on the morphological identification, these two species can be distinguished from one another by the shape and width of the leaf laminae and the length of a terminal stiff point of the leaf laminae; the type and position of the inflorescences and the number of flowers per inflorescence; the character and color of the bracteoles; the presence or absence of the flower pedicels; the shape of the mature flower buds; the shape, color, and texture of the sepals; the shape, character, and the presence or absence of hairs of the petals; the number of stamens per flower; the size of the fruits; the color and size of the hypocotyls; the color and diameter of the cotyledonous cylindrical tubes; and the color of the colleters and exudate. The thick cuticles, sunken stomata, large hypodermal cells, and cork warts are adaptive anatomical features of leaves in Rhizophora that live in the mangrove environments. The pollen grains of Thai Rhizophora species are tricolporate, prolate spheroidal or oblate spheroidal shapes, small-sized, and reticulate exine sculpturing.

A taxonomic revision of GarciniasectionGarcinia (Clusiaceae) in Thailand.

GarciniasectionGarcinia (Clusiaceae) is revised for Thailand with three species and one variety, i.e., two native species: G.celebica and G.exigua, and one cultivated species: G.mangostanavar.mangostana. Detailed morphological descriptions, illustrations, and an identification key to the species are presented, along with notes on distributions, habitats and ecology, phenology, conservation assessments, etymology, vernacular names, uses, and specimens examined. The section is recognized by its terminal inflorescences of simple cymes, or sometimes a solitary flower; flowers with 4 sepals and 4 petals; male flowers often with a pistillode, and stamens united into a single 4-lobed or 4-angled bundle, and with 2-thecous anthers; usually multilocular ovaries and stigmas with distinct or weak lobes and smooth or rough; and fruits with a smooth surface. Three associated synonyms of G.celebica: G.ferrea, G.basacensis, and G.hombroniana, are lectotypified here in a second-step. In Thailand, Garciniacelebica is found in a very wide variety of habitats, at elevations of 0-1,500 m amsl., and is known to be naturally distributed in all floristic regions. G.exigua is found in dry evergreen forest on limestone hills and in littoral dry evergreen forest on limestone hills, at elevations of 50-100 m amsl. in Krabi Province, the peninsular region. G.mangostanavar.mangostana is found only in cultivation. Garciniaexigua has a conservation status of Vulnerable [VU B2ab(iii)] and the other two species have a conservation status of Least Concern [LC]. The fleshy pulp surrounding the seeds of two species, G.celebica and G.mangostanavar.mangostana is edible and has a sweet-sour taste.

The use of Pisolithus albus found in saline areas to improve the growth of Eucalyptus seedlings under high salinity conditions.

Salinity is an abiotic factor limiting plant fitness and therefore forest crop productivity, and salt-affected areas have been expanding throughout the world. Ectomycorrhizal (ECM) fungi can improve the salt tolerance of woody plants, including Eucalyptus species To screen for salt-resistant Pisolithus albus (PA) isolates, 16 PA isolates were cultivated on modified Melin-Norkrans agar containing NaCl at concentrations of 0, 10, 20, and 30 dS m-1. The P. albus isolate PA33 had the greatest salt resistance under 10 and 20 dS m-1 NaCl, which are soil salinity levels in salt-affected areas of Thailand. We studied the effect of PA33 on Eucalyptus camaldulensis × E. pellita cuttings under salt stress (0 and 16 dS m-1) for 1 month. PA enhanced the growth of the Eucalyptus seedlings, as indicated by higher relative growth rates in height and root collar diameter of inoculated seedlings compared with non-inoculated seedlings. Moreover, the inoculated seedlings had less cell damage from NaCl, as indicated by significantly lesser leaf thickness and electrolyte leakage than the controls. These findings could lead to practices conferring socioeconomic and environmental benefits, as abandoned salt-affected areas could be reclaimed using such Eucalyptus seedlings inoculated with salt-tolerant ECM fungi.

A taxonomic revision of Garcinia section Xanthochymus (Clusiaceae) in Thailand.

Garcinia section Xanthochymus (Clusiaceae) is revised for Thailand with four native species, i.e., G. dulcis, G. nervosa, G. prainiana, and G. xanthochymus. All species are described with updated morphological descriptions, illustrations, and an identification key, together with notes on distributions, distribution maps, habitats and ecology, phenology, conservation assessments, etymology, vernacular names, uses, and specimens examined. Four taxa, G. andamanica, G. andamanica var. pubescens, G. cambodgiensis and G. vilersiana, are synonymized under G. dulcis, and two taxa, G. nervosa var. pubescens and G. spectabilis, are newly synonymized under G. nervosa. Nine names are lectotypified: G. dulcis and its associated synonyms (G. cambodgiensis and G. vilersiana), G. nervosa and its associated synonyms (G. andersonii, G. nervosa var. pubescens, and G. spectabilis), G. prainiana, and G. xanthochymus. All species have a conservation assessment of Least Concern (LC). The fruits of all species are edible and have a sour or sweet-sour taste.

Morphology, Taxonomy, Anatomy, and Palynology of the Opium Poppy (Papaver somniferum L.) Cultivation in Northern Thailand.

In this paper, we present the morphology, taxonomy, anatomy, and palynology of Papaver somniferum. A detailed morphological description and illustrations of the species are provided, along with information about the identification, distribution, cultivation areas, habitats, pollinators, specimens examined, growing periods, phenology, etymology, vernacular name, and uses. The species can be characterized as a glabrous and glaucous herb with unlobed or pinnately lobed leaves, and an amplexicaul base; variations in color and morphological characteristics of petals; and white filaments, occasionally purple with a white basal part, broadened at the apical part. Two rings of discontinuous and widely spaced collateral vascular bundles are recognized in the transverse section of the stems. The shape of epidermal cells on the adaxial surface is polygonal, while that on the abaxial surface is polygonal or irregular. The anticlinal cell walls of the epidermal cells on the adaxial surface are straight or slightly curved, while those on the abaxial surface are straight, slightly curved, sinuate, or strongly sinuate. The stomata are anomocytic and are confined to the lower epidermis. The stomatal density is 54-199/mm2 (with a mean of 89.29 ± 24.97). The mesophyll is not distinctly differentiated into palisade and spongy regions. Laticifers are found in the phloem areas of the stems and leaves. The pollen grains can be spheroidal or prolate spheroidal in shape, sometimes oblate spheroidal [polar axis (P) diameter/equatorial axis (E) diameter ratio = 0.99-1.12 (with a mean of 1.03 ± 0.03)]. The pollen aperture is tricolpate and the exine sculpturing is microechinate.

Morphology, Taxonomy, Culm Internode and Leaf Anatomy, and Palynology of the Giant Reed (Arundo donax L.), Poaceae, Growing in Thailand.

In this paper, we present the morphology, taxonomy, anatomy, and palynology of Arundo donax. A detailed morphological description and illustrations of the species are provided, along with information about the identification, distribution, the specimens examined, habitat and ecology, the International Union for Conservation of Nature (IUCN) conservation assessment, phenology, etymology, vernacular name, and uses. The species can be distinguished by its large, tall rhizomatous perennial reed; cauline leaves; an open, large, plumose panicle inflorescence; subequal glumes as long as the spikelets; glabrous rachilla; all bisexual florets; and a lemma with a straight awn and with long white hairs outside below the middle part. In this study, two names were lectotypified: Arundo bifaria and A. bengalensis, which are synonyms of A. donax. The culm internodes in the transverse section have numerous vascular bundles scattered in the ground tissue, and the parenchyma cells have significantly lignified cell walls. Vascular bundles are composed of phloem and xylem and are enclosed in a continuous sclerenchymatous bundle sheath. The chloroplasts in the transverse section of the leaf blades are found only in the mesophyll cells but are absent in the bundle sheath cells, which indicates that it is a C3 grass. The leaves have stomata on both surfaces and are confined to the intercostal zones. The stomata are typically paracytic, with two lateral subsidiary cells placed parallel to the guard cells. The stomatal density is higher on the abaxial surface [450-839/mm2 (606.83 ± 72.71)] relative to the adaxial surface [286-587/mm2 (441.27 ± 50.72)]. The pollen grains are spheroidal or subspheroidal [polar axis length/equatorial axis length ratio (P/E ratio) = 0.89-1.16 (1.02 ± 0.07)] with a single pore surrounded by a faint annulus, and the exine sculpturing is granular.

Assessing the Cooling and Air Pollution Tolerance among Urban Tree Species in a Tropical Climate.

We present the results of classifying plants at species level that can tolerate air pollution, provide cooling, and simultaneously survive and thrive in urban environments. For this purpose, we estimated the air pollution tolerance index (APTI) and anticipated performance index (API) of several species growing in a park located in central Bangkok, Thailand. The cooling effect was quantified by calculating the reduction in soil and air temperatures. Melaleuca quinquenervia (Cav.) S.T. Blake, Albizia saman (Jacq.) Merr., Chukrasia tabularis A. Juss. had the highest API score and were able to substantially reduce the temperature and were in a group of highly recommended species which also included other species like A. saman, C. tabularis, Tabebuia rosea (Bertol.) Bertero ex A. DC., Dalbergia cochinchinensis Pierre etc. Species from both evergreen and deciduous habitat were able to provide ambient cooling but were vulnerable to air pollution and included Elaeocarpus grandifloras Sm. and Bauhinia purpurea L. However, there were other species which had a high air pollution tolerance but failed to provide adequate cooling, such as Hopea odorata Roxb. and Millingtonia hortensis L.f. The results would be of interest to urban greenspace landscapers in such climates while selecting suitable species that can provide multiple ecosystem services ranging from air pollution tolerance to temperature reduction without reducing plant vitality.

Variations in mitragynine content in the naturally growing Kratom (Mitragyna speciosa) population of Thailand.

We analyzed the content of mitragynine (MG) found in kratom leaves (Mitragyna speciosa) and the influence of different environmental conditions (air and soil variables) on the yield in various regions of Thailand. The content of MG in kratom leaves ranged from 7.5 - 26.6 mg g-1 of dry leaf weight. Canonical correspondence analysis showed that the most significant environmental variables affecting the MG content among the various regions were light intensity, relative humidity, soil volumetric water content (VW), soil pH, and calcium. This study is a first step towards providing information about environmental conditions suitable to maximize the quality and quantity of bioactive alkaloids in kratom. Future studies should focus on leaf collection and the post-harvest processes in order to assure the desired alkaloidal content in finished products, when produced under suitable environmental conditions identified in this study.

Comparison of water-use characteristics of tropical tree saplings with implications for forest restoration.

Tropical forests are experiencing reduced productivity and will need restoration with suitable species. Knowledge of species-specific responses to changing environments during early stage can help identify the appropriate species for sustainable planting. Hence, we investigated the variability in whole-tree canopy conductance and transpiration (Gt and EL) in potted saplings of common urban species in Thailand, viz., Pterocarpus indicus, Lagerstroemia speciosa, and Swietenia macrophylla, across wet and dry seasons in 2017-2018. Using a Bayesian modeling framework, Gt and EL were estimated from sap flux density, informed by the soil, atmospheric and tree measurements. Subsequently, we evaluated their variations with changing vapor pressure deficit (VPD) and soil moisture across timescales and season. We found that Gt and EL were higher and highly variable in L. speciosa across seasons than S. macrophylla and P. indicus. Our results implied that water-use in these species was sensitive to seasonal VPD. L. speciosa may be suitable under future climate variability, given its higher Gt and EL across atmospheric and soil moisture conditions. With their lower Gt and EL, P. indicus and S. macrophylla may photosynthesize throughout the year, maintaining their stomatal opening even under high VPD. These findings benefit reforestation and reclamation programs of degraded lands.

Investigating carbon dioxide absorption by urban trees in a new park of Bangkok, Thailand.

BACKGROUND: Trees remove atmospheric carbon dioxide through photosynthesis, hereafter CO2 absorption (A). Despite growing urban green areas, only a few studies have quantified A of urban trees and assessed their dynamical changes with varying atmospheric conditions. Hence, we investigated A in nine dominant tree species in a new park of Bangkok. RESULTS: Results revealed that A of two tree species (Millingtonia hortensis and Afzelia xylocarpa) significantly increased with vapor pressure deficit (VPD) until it reached a maximum and declined when VPD decreased, with no seasonal difference. Five of them (Dalbergia cochinchinensis, Tabebuia rosea, Lagerstroemia floribunda, Dipterocarpus alatus and Bauhinia purpurea) exhibited different response patterns of A to VPD between wet and dry seasons. In contrast, the A of two tree species (Samanea saman and Homalium tomentosum) did not respond to changing VPD in either season. CONCLUSIONS: Comparing planting scenarios of insensitive (i.e. no response to VPD) versus sensitive (i.e. significant response to VPD) species, we found that planting a mixture of sensitive and insensitive tree species would improve the park's capacity of A across seasons, allowing climate change adaptation to adverse environmental impacts such as droughts and the urban heat island effects, and would increase biodiversity. Additionally, planting insensitive tree species would significantly increase the capacity of the park for CO2 mitigation. These findings are useful for those who design parks and expand urban green areas to fully benefit ecosystem services from trees.