New records for the flora of Angola: observations from Uíge and Cuanza Norte

Background and aims – Located in the transition zone of Guineo-Congolian and Zambezian phytochoria, the Angolan provinces of Uíge and Cuanza Norte are of particular interest for floristic studies and high biodiversity is expected. Nevertheless, explorations of the vegetation are relatively rare. Our study aims to supplement a recent checklist of vascular plants of Angola. Methods – Data were collected during 17 field trips between 2013 and 2018, during which herbarium specimens were prepared for later identification of plant species. The results were compared with the current checklist as well as with other floristic works, herbarium collections and online databases relevant for the region. Key results – We document 20 new records of indigenous vascular plant species for the flora of Angola (19 species and one subspecies), including four new generic records. Furthermore, nine alien species are added to the checklist of the flora of Angola. Conclusion – Our results confirm that the flora of northern Angola is composed by elements of various adjacent areas. However, not all species present are known yet. Further botanical investigation is needed to complete our floristic knowledge of the region.


INTRODUCTION
Explorations of the vegetation of Angola are relatively rare (Dauby et al. 2016). First scattered collections date back to the 17 th century (Goyder & Gonçalves 2019). Subsequently, several explorers studied the flora of the coastal plain and some interior parts of the country. Among them the Austrian Friedrich Welwitsch (1806-1872), the German Hugo Baum , and the Swiss Johannes Gossweiler (1873Gossweiler ( -1952 rank as the most important. Further valuable collections were made from the late 1950s to 1974, by Portuguese collectors such as Eduardo José Santos Moreira Mendes (1924-2011), Joaquim Martinho Lopes de Brito Teixeira (1917-1969 and Luis A. Grandvaux Barbosa (1914Barbosa ( -1983. António Rodrigues Fonseca Raimundo (1926Raimundo ( -2014 actively collected plants in Uíge. Notwithstanding their extensive surveys, the north of Angola is still underrepresented in herbarium collections, not least because of wars lasting forty years and preventing any continuous botanical or ethnobotanical investigations (Figueiredo & Smith 2008;Sosef et al. 2017).
Following Brummitt (2001), Angola is part of South Tropical Africa. The Northern Province of Uíge borders the Democratic Republic of the Congo (further D.R. Congo) in the north and east, the Angolan provinces of Malanje, Cuanza Norte and Bengo in the south, and the Zaire province in the west. While most of the country is characterized by different savannah types, Uíge as well as parts of Cuanza Norte belong to the ecoregion called Western Congolian Forest-Savannah Mosaic (Olson et al. 2001). White (1983) concretised that elements of both the Guineo-Congolian and the Zambezian Regions are forming a Regional Transition Zone of high complexity. Even some pure Congolian forest patches exist along the big rivers such as the Cuango (Goyder & Gonçalves 2019). However, White (1983) depicted this area as grassland and wooded grassland secondarily formed following the destruction of the original vegetation.
Recent studies provide a more detailed picture of the area. During field trips in Uíge and Cuanza Norte we collected and identified 820 species of mosses (Müller 2015;Müller et al. 2019), ferns, gymnosperms and angiosperms being stored now in the Herbarium Dresdense (DR). In the mountain chain of Serra Pingano, an unknown Impatiens species was found and described as Impatiens pinganoensis Abrah. et al. (Abrahamczyk et al. 2016). Furthermore, ethnobotanical surveys from the region were published during the last years (Göhre et al. 2016;Heinze et al. 2017;Lautenschläger et al. 2018).
The checklist of vascular plants of Angola (Figueiredo & Smith 2008) comprises 6735 native and 226 non-native species (Figueiredo et al. 2009;Smith & Figueiredo 2017). Here, we present new records of another 19 species and one subspecies as well as of nine alien species.

MATERIALS AND METHODS
The data were collected during 17 field trips from 2013 to 2018. Data sampling was carried out between 5°58′59.2″S and 9°40′60.5″S and between 14°10′37.0″E and 16°17′04.5″E ( fig. 1). All the surveys were permitted and accompanied by the local authorities. The Ministry of the Environment, Republic of Angola, and the Province Government of Uíge issued the required collection and export permits. For documentation, plant voucher specimens, complemented by photographs, were collected, dried and stored at the Herbarium Dresdense (DR), Technische Universität Dresden, Germany. Voucher specimen numbers are given in the checklist below. All sample data are available at Virtual Herbaria JACQ (https://herbarium.univie.ac.at/database/). Due to CITES trade regulations one orchid species is documented by photo voucher only. In a Memorandum of Understanding signed in 2014, the Instituto Nacional da Biodiversidade e Áreas de Conservação (INBAC), Angola, and the Technische Universität Dresden, Germany, agreed upon that duplicates of herbarium vouchers will be returned to Angola as soon as appropriate conditions to store them are established. Identification of collected plant specimens and data analysis were completed in Dresden. For identification, relevant floristic works were used and listed in the particular species description.
Furthermore, for some plant groups, specialists were consulted. Plant families are treated alphabetically.

RESULTS
Based on the checklist of the vascular plants of Angola (Figueiredo & Smith 2008), we present records of 20 native species new to the flora of Angola including three new genera (Epithema, Mendoncia, Newbouldia), and 9 neophytes (three new genera: Eleutherine, Eryngium, Leptaspis). Habitat -Rain forest. Notes -The light mauve flowers are comparatively large with a corolla up to 5 cm. It keys out next to Asystasia scandens (Lindl.) Hook. from which it differs by its inflorescence being longer and less dense. Additionally, its corolla tube is much longer and not suddenly widened to become bellshaped in the upper two thirds, like in A. scandens.
Habitat -Rain forest. Notes -The specimen is characterized by a long indumentum along the stem, the petioles and veins. The bracteoles are predominantly hispidly hairy, the pedicel is shorter than 15 mm ( fig. 2E). The species is otherwise known from Cameroon, Equatorial Guinea, Gabon and highly disjunct from eastern Congo (Kinshasa). This is the first record of the genus Mendoncia in Angola. Reference -Crusio (1979).
Habitat -Understory of cloud forest. Notes -A number of African Impatiens species is characterized by spirally arranged leaves with petioles at least 1 cm long and up to 10 lateral veins, a much-reduced peduncle and a navicular lower sepal being abruptly constricted into a short filiform spur. Within this group, I. burtonii keys out by usually pubescent, 3-4 mm long lateral sepals without glandular teeth, petioles which are not fimbriate-glandular, lateral united petals without a filiform appendage extending into the spur and a relatively large flower size (

Begoniaceae
Begonia johnstonii Oliv. ex Hook.f. Distribution -East Tropical Africa. Habitat -On rocks. Notes -Determination of Begonia johnstonii was carried out by a specialist (M. Hughes, Royal Botanic Gardens, Kew, UK, pers. comm. 2018). Up to now, this species was only known from Kenya and Tanzania. Taking into account the dust-like seeds freely floating in the air, some anemochorous long distance dispersal may have spread the seeds from eastern Africa to Angola, where again suitable habitats on rocks within the forest may have facilitated successful establishment. According to Plana et al. (2004) the present distribution of Begonia johnstonii, B. engleri Gilg and B. annobonensis A.DC. could be the result of a climate change during the early Pliocene leading to rainforest expansion and isolating the populations of the three Begonia species which they described as functionally annual and well adapted to more seasonal conditions. In this case, the Angolan Begonia johnstonii might as well represent another relict population (

Calvoa seretii De Wild. subsp. seretii Distribution -West Central Tropical Africa.
Habitat -Swampy forest. Notes -Glabrous herb, leaf lamina longer than 3 cm, attenuate at base, apex acute. The capsules of the specimen exhibit a 5-lobed crown, exserted for only 1.5 mm. The petal lobes are reddish. Notes -The specimens exhibit heteromorphic leaves up to 9 cm long with distinct petioles up to 15 mm. The corolla is large (3 cm) but never achieves 7 cm (Sesamum angolense Welw.). The blades of the specimens also differ from those of S. angolense (broad, blunt tips, more hairy). S. radiatum was mentioned for Angola in the Flore du Gabon (Bedigian 2011), but up to now no herbarium specimen was known from this country, according to D. Bedigian (Missouri Botanical Garden, USA, pers. comm. 24 Jul. 2019).

Leptaspis zeylanica Nees
Distribution -South Tropical Africa, West Tropical Africa, West Central Tropical Africa, Northeast Tropical Africa, East Tropical Africa, Western Indian Ocean. Habitat -Understory of rain forest. Notes -The achenes of this forest grass are enclosed in inflated conchiform lemmas densely covered by minute hooked hairs which favour epizoochory. Leptaspis zeylanica is a widespread species that also occurs in Madagascar and further east across to the Solomon Islands (Soderstrom et al. 1987). Nevertheless, this is the first record of the genus Leptaspis in Angola. Habitat -In a village, likely escaped. Notes -In contrast to Acanthospermum hispidum DC. hitherto recorded from Angola (Figueiredo & Smith 2008) the achenes of this species lack two large erect apical spines. The website Invasive Species Compendium (CABI 2019) documented unintentional vector transmission by humans or animals for this species and identified it as potentially invasive.  15°05′39″ E, 930m, 10 Nov. 2014, T. Lautenschläger 2014 15°11′15″E, 977m, 25 Nov. 2015, T. Lautenschläger 2015. References - Blake (1921); Adams (1963): under the synonym Acanthospermum brasilum Schrank; Wild (1967); Lisowski (1991).

Galinsoga quadriradiata Ruiz & Pav.
Distribution -Central America, South America. Habitat -In a village, likely escaped. Notes -So far, only Galinsoga parviflora Cav. is recorded for Angola (Bossard 1996). Compared to this species the stems of G. quadriradiata are hispid with long spreading hairs and long-stalked glands (not glabrous or nearly so), the receptacle scales are simple to shortly laciniate (not trifid), and the pappus scales are shorter than the corolla of the disc florets (notlonger). Schulz (1981)

Ipomoea hederifolia L.
Distribution -Central America, South America. Habitat -Secondary rain forest. Notes -The salver-shaped, brightly scarlet flowers with distinctly awned sepals differ clearly from all the 48 Ipomoea species Figueiredo & Smith (2008a) compiled for Angola. I. hederifolia is an annual plant long known to occur as an ornamental weed in many tropical countries including parts of Africa (see references). In contrast to I. purpurea (L.) Roth and I. tricolor Cav. Gossweiler (1950) did not mention it as a subspontaneous ornamental from garden cultivation in Angola. Lejoly & Lisowski (1992) listed herbarium specimens of I. hederifolia from various regions of the D.R. Congo. They include Angola into the area of distribution, but no proof is given for the occurrence of the species there. CABI (2019) identified this species as potentially invasive.

DISCUSSION
The main objective of our investigations was to collect and document ethnobotanical knowledge, not to carry out comprehensive floristic field studies on biodiversity. However, the results presented indicate that new records are very likely to be documented with ongoing field work and botanical exploration in northern Angola. According to Olson et al. (2001) four ecoregions important for conservation of global biodiversity are less than 1000 km away from Uíge, the centre of our present study: Congolian Coastal Forests (300 km to the northwest), Western Congo Basin Moist Forests and Central Congo Basin Moist Forests (700 km to the north and northeast respectively), and the Central and Eastern Miombo Woodlands (800 km to the east and south). Being part of a transition zone, remnant forests, woodlands and savannahs in the study area provide suitable habitats for isolated populations of plants from all these ecoregions. Our knowledge of the species richness and the composition of fauna and flora of northern Angola is still limited (Figueiredo & Smith 2008;Goyder & Gonçalves 2019). Further studies must prove whether the relevance of the area in the context of global biodiversity conservation may be higher than estimated so far, especially as Angola is one of the botanically least explored countries in Sub-Saharan Africa (Sosef et al. 2017).
All of the nine new records of alien species presented here originate from the Neotropics. The strong historical connection between the West coast of Africa and the New World might explain this fact. Slaves from Angola were shipped to Brazil, both Portuguese colonies; plants with an economic value were transferred to Africa. But even before the peak of slave trade was reached in the 18 th century a botanical homogenization between the two continents had taken place. The environmental historian Crosby (2003) termed the early transatlantic trade of slaves, livestock and cultivated plants "Columbian Exchange". A transculturation of plant use traditions in Africa as well as America was one of its manifold profound effects (Voeks 2013).
Eight of the nine newly recorded alien species can be classified as weeds that were introduced to the region unwillingly. However, the distribution paths are difficult to reconstruct. Nevertheless, as five of the here listed nine species are classified as potentially invasive (CABI 2019), strong efforts to avoid their further distribution need to be undertaken.

ACKNOWLEDGEMENTS
The University Kimpa Vita was an essential base for our field work and provided logistical support. The authors would like to thank Dorothea Bedigian, Iain Darbyshire, Friedrich Ditsch, Stefan Dressler, Mikhail Goncharov, Paul Hoekstra, Mark Hughes, Markus Lehnert, Christian Schulz, and Jan Wieringa for assistance in the identification of selected herbarium specimens. We are also grateful to the Herbarium LISC in Lisbon and the Herbarium COI in Coimbra, Portugal for the assistance as well as to the Botanical Garden of the TU Dresden for cultivating plants until essential characters for identification appeared. We thank the reviewers for their very valuable recommendations. The fieldwork in Angola was supported by a travel fund from the German Academic Exchange Service (DAAD) and the program 'Strategic Partnerships' of the TU Dresden. These published results were obtained in collaboration with the Instituto Nacional da Biodiversidade e Áreas de Conservação (INBAC) of the Ministério do Ambiente da República de Angola. Since 2012 the Universidade Kimpa Vita in Uíge, Angola and the Technische Universität Dresden, Germany, have a multifaceted cooperation including the establishment of a Botanical Garden with the focus on the documentation of local medicinal plants as well as biodiversity assessments.