Floral morphology, anatomy and development are examined in Xyris grandis (Xyridaceae: Poales), with an emphasis on petal and sepal organogenesis and vasculature. Xyris is one of relatively few monocots in which the perianth is differentiated into two distinct whorls (here termed a double perianth). Xyris also possesses highly unusual perianth vasculature, with each petal being supplied by three veins and each sepal by a single vein, compared with the opposite condition in most other angiosperms with a double perianth. However, perianth development in X. grandis shows a pattern that is typical for monocots, with petals not markedly delayed in development. Xyris grandis is also remarkable for its petal aestivation, with each petal surrounding a stamen and two branches of adjacent staminodes, a type that is not reported for other Xyridaceae and may contribute to secondary pollen presentation. The results are discussed in the context of the diversity of a double perianth in monocots, compared with eudicots. Based on current data, our preferred hypothesis is that meristic differences are at least partly responsible for the apparently widespread occurrence of three‐traced petals in monocots. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 93–111.

Biermannia King & Pantling (1898a: 591) comprises about ten species distributed from northeastern India and southern China through the Indochinese and Malay Peninsulas to Sumatra, Java and Borneo (Comber 1990, 2001, Seidenfaden & Wood 1992, Pearce & Cribb 2002, Chen & Wood 2009, Chase et al. 2015). All species of this genus are miniature, canopy epiphytes with small, unattractive fugacious flowers lasting only few hours in the morning. As a result, representatives of this genus are easily overlooked in botanical surveys, poorly represented in herbaria and remain infrequently inventoried in local floras throughout its range. One more new species that differs strikingly from all hitherto known species of this genus was recently discovered in southern Vietnam. Here we describe and illustrate this unusual plant.

Thismia mucronata, a new species of Thismiaceae, is described and illustrated. The species was discovered in 2013 during a botanical survey of a forest in the vicinity of Bao Loc town (Lam Dong province, Southern Vietnam). Thismia mucronata is characterised by vermiform roots and mitriform inner tepals. It differs from related species mainly by the short and appressed to each other appendages of inner tepals, which together resemble a short mucro, the narrow mitre without foveae, the almost horizontal annulus and the absence of interstaminal glands. A key to Vietnamese species of Thismia is provided.

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One following the news of systematics of the genus Aspidistra Ker Gawler (1822: 628) should notice that the year 2016 brought us at least 16 new taxa, including 15 new species and one subspecies (Averyanov & Tillich 2016, Averyanov et al. 2016, Liang et al. 2016, Liu et al. 2016, Ly & Tillich 2016, Pan et al. 2016, Tanaka 2016, Vislobokov 2016, Vislobokov et al. 2016a, 2016b, Zhou et al. 2016). Indeed, Aspidistra is a large and rapidly growing genus which comprises about 160 species, including more than 60 of them known in Vietnam (e.g., Tillich 2005, 2008, 2014, Averyanov & Tillich 2015, 2017, Colin 2015, Vislobokov 2015, 2016, Averyanov et al. 2016, Vislobokov et al. 2016a, 2016b).

Aspidistra corniculata is described and illustrated here as a new species from northern Vietnam. In flower structure, A. corniculata resembles A. lubae, A. marasmioides, A. multiflora and A. zinaidae but possesses hornlike connective appendages in stamens that distinguish it from all the other close species.

Elatostema (Urticaceae) comprises several hundred herbaceous species distributed in tropical and subtropical Africa, Asia, Australia and Oceania. The greatest species richness occurs on limestone karst in Southeast Asia. Taxonomic revisions of Elatostema are largely out of date and contradict each other with respect to the delimitation of Elatostema and Pellionia. Most herbaria in SE Asia and worldwide contain significant amounts of unidentified material. As part of a broader revision of Elatostema in SE Asia, we present an updated checklist for Vietnam based on field visits, a review of specimens in herbaria worldwide, a review of type material and nomenclature. We recognize 77 taxa (75 species and two infraspecific taxa) of Elatostema in Vietnam, 23 of which were previously ascribed to Pellionia. Nineteen of these are new records for the country, i.e., E. attenuatoides, E. austrosinense, E. backeri, E. brunneinerve, E. crassiusculum, E. crenatum, E. fengshanense, E. glochidioides, E. malacotrichum, E. nanchuanense, E. oblongifolium, E. obtusum, E. oppositum, E. pergameneum, E. prunifolium, E. pseudolongipes, E. pycnodontum, E. salvinioides and E. xichouense. We place E. baviensis in synonymy of E. platyphyllum, E. colaniae in synonymy of E. myrtillus, P. macroceras in synonymy of E. hookerianum, and P. tetramera in synonymy of E. dissectum for the first time. Fourteen taxa (18% of all the recognized taxa) are endemic to Vietnam, which makes Elatostema one of the richest genera for endemic species in this country; this level of endemism is comparable to levels observed in Orchidaceae. Our checklist suggests that the highest diversity and endemism of Elatostema occurs in northern Vietnam, and that there is the greatest floristic similarity of northern Vietnam to SW China. The relationship among floristic regions is also investigated. We could find no records of Elatostema for 33 out of 63 provincial units of Vietnam, including all the southernmost provinces. We propose that further studies on the diversity of Elatostema in central and southern Vietnam are severely needed.

The family Petrosaviaceae is represented by two species in Vietnam, viz. Petrosavia sakuraii restricted to the northern part of the country and P. stellaris distributed in its southern part. The latter species is shown to possess a wide range of distribution in Vietnam, though it was previously believed to be an exclusively Malesian species. The inclusion of P. sinii in P. sakuraii is confirmed. Details on distribution, illustrations and an identification key for these species are provided.