A foundation monograph of Ipomoea (Convolvulaceae) in the New World

Endemism
Throughout the Americas many species are endemic to single countries with a good number of species endemic to single localities or to a very restricted area. Clearly the two largest countries, Brazil and Mexico, each with about 60 endemic species, have the greatest numbers of single country endemics. Scattered endemic species are found in most Andean countries with much the greatest numbers in Bolivia (c. 20) but the arbitrary nature of political boundaries tends to reduce the gross figures for individual countries. There are few species endemic to the small Central American republics although four are endemic to the Panama-Guatemala region. The large Caribbean islands are also major centres of endemism. We recognize 17 species as endemic to Cuba, seven to Hispaniola and four to Jamaica. Additionally there are a number of near endemics on these islands. In contrast, species endemic to small islands or island groups are few and we recognize only four, Ipomoea sphenophylla on St Eustatius, I. steudelii on Puerto Rico, I. tuboides on Hawaii and I. habelana on the Galapagos, the last two on several islands in their respective archipelagos and, perhaps coincidentally, both adapted for moth pollination.
It is harder to discern concentrations of endemic species in particular regions of the large continental countries, particularly in Mexico, where endemic species occur in scattered locations over much of the country. However, there is evidence that the greatest concentrations of endemics are in the seasonally arid regions of South West Mexico (McDonald 1991), with a lesser centre in the central northern plateau. Much the same is true for South America but the Chapada de Veadeiros (Brazil) is home to at least four endemic species and the Sierra de Amambay (Paraguay) to at least three. Both these locations are also home to several other very rare species which extend only to a few nearby locations. Another very rich area comprises the lower eastern slopes of the Andes near the border of Argentina and Bolivia. This is exceptionally diverse in terms of local endemic species with at least nine species endemic to the area.
It is equally difficult to discern clear examples of endemism in particular biomes except for some extreme examples such as seashores. Clearly there are many species endemic to Seasonally Dry Forest and to Cerrado but as the former includes many distinct variants and the latter very different physiognomies from campo limpo to cerradão, the notion of endemism is not very easy to apply except in a very loose sense. Specific examples of habitat preferences are indicated after species descriptions, where these are reliably known.
Ecology
Precise information about the ecology of many species is unavailable so it is difficult to provide anything approaching a comprehensive account of the habitat requirements of many neotropical species. Certainly, Ipomoea species grow in many different habitats and it is clear that most habitats host species specific to that habitat.
The most typical beach species are Ipomoea pes-caprae, I. imperati and I. littoralis (in Hawaii) but others occur on coastal sands including I. tiliifolia and some forms of I. batatas. There is some evidence that the fruits of some of these species can survive for long periods in salt water (Miryeganeh et al. 2014) and it has been suggested that in the case of I. pes-caprae the persistent pedicel actually aids seed dispersal. The world distribution of these species and that of I. violacea, which often grows in mangrove swamp, strongly suggests that their dispersal is mediated through ocean currents. This may be the explanation of how the salt marsh species, I. sagittata made it to Europe in prehistoric times. Ocean currents may also partially explain the distribution of Ipomoea indica and I. triloba as both show a predilection for islands, although the former is also readily spread by broken shoots as a result of trampling by cattle. There is also an interesting group composed of species that are not strictly maritime but are often found in the proximity of the coast, although all occur, sometimes abundantly inland; these include Ipomoea tiliacea, I. mauritiana, I. digitata, I. asarifolia, I. macrorhiza and I. jalapa.
Some species are characteristic of freshwater habitats and are often specialized in their requirements. The only true aquatic is the introduced Ipomoea aquatica, which roots on mud and sometimes has extensive floating stems. Ipomoea subrevoluta usually grows by small streams in grassy plain whereas I. rubens is more typical of the borders of larger rivers or small lakes. Ipomoea paludicola, I. schomburgkii and I. pittieri favour flooded pampa whereas I. paludosa is characteristic of swampy hollows in the cerrados. Ipomoea fimbriosepala, I. setifera and I. neei are often found near water. The widespread species I. alba appears to favour disturbed scrubby gullies which are permanently or seasonally moist, when it grows as an apparently native species. The natural distribution of I. carnea subsp. fistulosa is obscured by its presence as an escape from cultivation but it appears native in swamp in the Parana basin of South America and perhaps elsewhere.
The lack of diversity of Ipomoea in rain forest does not mean that there are no characteristic species in this habitat. The best indicator of rainforest in the genus is I. philomega, which is found in evergreen forest at low altitudes throughout the Americas. Other typical species that are more local in their distribution include I. amazonica, I. velutinfolia, I. santillanii, I. splendor-sylvae whereas I. aurantiaca, I. chondrosepala, I. regnellii, I. squamosa, I. batatoides and I. reticulata also occur in rainforest but are not restricted to this habitat. The near absence of several otherwise widespread species from the Amazon basin is also interesting. Ipomoea hederifolia and I. carnea subsp. fistulosa are almost completely absent from Amazonia.
Cloud forest is another wet forest habitat where Ipomoea is relatively poorly represented. Cloud forest occurs from slightly below 1000 m to at least 2500 m along the Andes from Bolivia northwards, in the Brazilian Atlantic forest and in Central America. Probably the most widespread cloud forest species is I. lindenii, which grows from Bolivia to southern Mexico with an outlying station in Jamaica. Other cloud forest species are much more local but include I. austrobrasiliensis from the Brazilian Atlantic Forest, I. magnifolia, I. inaccessa and I. odontophylla from the Bolivian Andes, I. retropilosa from Colombia and Venezuela, I. chiriquensis, I. isthmica from Panama and Costa Rica and I. chenopodiifolia from Guatemala and Mexico. Other species may occur in coffee plantations, which are often created from areas of former cloud forest including the widespread I. aristolochiifolia.
High altitude species are even rarer and very few species occur above about 2500 m. The only species that might occur in paramo is Ipomoea capillacea while, in puna or at least subpuna, the only species recorded are I. plummerae and I. pubescens. Both have a disjunct amphitropical distribution occurring in Mexico and the United States Southwest as well as South America. Ipomoea plummerae reaches 4000 m in Bolivia.