﻿A taxonomic revision of Cenchrus L. (Poaceae) in Thailand, with lectotypification of Pennisetummacrostachyum Benth.

﻿Abstract A revision of the genus Cenchrus (Poaceae) in Thailand is reported. Seven species, i.e. C.brownii, C.ciliaris, C.clandestinus, C.echinatus, C.pedicellatus, C.purpureus and C.setosus are described in this taxonomic treatment. This genus is an exotic species and distributed throughout the floristic regions. All the species have become naturalised to Thailand as a weed and found growing in wastelands, open areas by the roadside, disturbed sites, the edge of rice fields and the edge of deciduous and evergreen forests at elevations between 0 and 2,650 m alt. Pennisetummacrostachyum, a synonym of Cenchruspurpureus is lectotypified. Detailed morphological descriptions, illustrations and a key to the species are presented, along with information on distributions, habitats, ecology, phenology, vernacular names and specimens examined.


Introduction
The Poaceae or grass family, also known as Gramineae, is one of the largest families of flowering plants, consists of approximately 12,000 species in 789 accepted genera and is widely distributed around the world (Soreng et al. 2022).This family is able to adapt to a wide range of habitats as it can survive in different environmental stresses.Grasses are both common and important plants.The world's human population relies on grasses, which include rice, wheat, oat and maize and are a valuable source of food for humans as they contain fibres, proteins and some nutrients.Most of them have a short life, fast growth and undergo high biomass accumulation.As such, several species are considered as good fodder and a source of nutrients for the livestock.Many species are also used as ornamental plants in landscaping and gardening, for beautifying the lawns.In addition, some grasses are used as raw materials in manufacturing paper, extracting the essential oils and are also used to prevent soil erosion and surface run-off (Chase 1921;Bor 1960;Gould 1968;McIlroy 1972;Oyen and Dung 1999;Obi Reddy et al. 2014;Chavre and Sonawane 2021).
Grasses have various morphological characters.Their reproductive part consists of a small spikelet which is a significant characteristic used in their

Material and methods
The study was based on the herbarium specimens of the following Herbaria: AAU, BK, BKF, BM, C, CMUB, K, KKU, P, PSU and QBG, including digital specimen images from B, BISH, E, G, LINN, S and W. Additional specimens were collected on recent field surveys made throughout Thailand.Plant morphological characters, ecological data and flowering and fruiting periods were also recorded.Most of the grass specimens collected from fieldwork have been submitted to BK and BKF.The identifications were made using morphological characters observed using a stereomicroscope and the available taxonomic literature available in Thailand and the neighbouring region.

Cenchrus ciliaris
Distribution.Native to Africa, Greece, Sicilia, Middle East, Afghanistan, Pakistan, India and Bangladesh.Introduced to America, Australia and Southeast Asia.

Habitat and ecology.
In open areas by the roadside and the edge of rice fields.This species is cultivated for forage at elevations between 0 and 250 m a.m.s.l.Flowering and fruiting from May to September.

Cenchrus echinatus
Distribution.Native to North America and South America.Introduced and naturalising elsewhere in tropical and temperate zones worldwide.
Distribution.Native to India and Tropical Africa and introduced to Indo-China, Malaysia, Australia, North America and South America.

Figure 3 .
Figure 3. Cenchrus ciliaris L. A habit B ligule C spikelets with involucre D lower glumes E upper glumes F lower lemmas G lower paleas H upper lemmas I upper paleas J caryopsis.Drawn from P. Wessapak 376 by Paweena Wessapak.

Figure 6 .
Figure 6.Cenchrus echinatus L. A habit B ligule C spikelets with involucre D lower glumes E upper glumes F lower lemmas G lower paleas H upper lemmas I upper paleas J caryopsis.(Drawn from P. Wessapak 361 by Paweena Wessapak).

Figure 12 .
Figure 12.Lectotype of Pennisetum macrostachyum Benth.Digital image The Board of Trustees of the Herbarium of the Royal Kew Botanic Garden (K).

Figure 13 .
Figure 13.Cenchrus setosus Sw.A habit B ligule C spikelet with involucre D spikelet E lower glumes F upper glumes G lower lemmas H lower paleas I upper lemmas J upper paleas K stamens L pistil M caryopsis.(Drawn by Paweena Wessapak).