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

Species delimitation
The history of species recognition in Ipomoea is somewhat chequered. Good taxonomic decisions always require an awareness of previous publications as well as a good understanding of the relative value of different taxonomic characters. Access to a good range of specimens and images as well as field knowledge are also useful but only a few taxonomists have been able to benefit from these. Most have worked with limited material. The new species of early authors have not always stood the test of time (Wood 2017). However, amongst those publishing a significant number of new species of neotropical Ipomoea, it is clear that both Desrousseaux and Kunth demonstrated a high degree of competence, avoiding excessive duplication of names and so most of their species have endured.
The legacy of the most important 19^th century expert on Ipomoea, the Swiss botanist Choisy, is very mixed and he was criticised even during his own lifetime. He saw a wide range of specimens in many European herbaria and was well aware of previous publications, but neither his generic nor his species concepts have lasted well. He described the same species under different names often in different genera (Choisy 1845). Ipomoea indica was described under at least eight different names, mostly in Pharbitis and I. batatas under at least four names in Batatas but also in Ipomoea. Similarly I. asarifolia was described under three names in Ipomoea, I. eriocalyx twice, once in Pharbitis once in Batatas, I. delphinioides three times in Ipomoea and so on.
The next major work was the account of Convolvulaceae prepared by Meisner (1869) for the Flora Brasiliensis and this was virtually a monograph of the family in South America. It was as unsatisfactory as Choisy’s works but for different reasons. Meisner appears to have largely discounted the names of earlier authors including those of Choisy. He superfluously redescribed species as if earlier publications did not exist - Ipomoea chrysotricha Meisn. instead of I. hirsutissima Gardner, I. obtusiloba Meisn. and I. heterotricha Meisn. instead of I. bonariensis Hook., I. riedelii Meisn. instead of I. batatoides Choisy, I. graminiformis Meisn. instead of I. schomburgkii Choisy, I. llaveana Meisn. instead of I. funis Schltd. & Cham., I. cardiosepala Meisn. instead of I. philomega (Vell.) House) and many others. The other major problem with his approach was the recognition of a large number of varieties under each species, a process that tended to obscure the boundaries of recognized species. These varieties often recognize trivial variation but, in contrast, in other cases treat distinct, often very distinct, species as mere varieties of unrelated species.
The inadequate species level taxonomy of Choisy and Meisner was not an inevitable consequence of the epoch in which they worked. Near contemporaries such as Grisebach (1862a, b, 1879) or Gray (1878, 1886 were far more reliable. However, the excessive recognition of varieties continued to bedevil species level taxonomy into the 20^th century in the publications of Kuntze (1891, 1898), Hallier (1899c) and especially of Chodat and Hassler (1905) and Hassler (1911). Hassler took this interest in infraspecific taxa to an obsessive level, providing names for every slight variant found in Paraguay. However, the publications of the North Americans, especially House (1907 and passim), Brandegee (1889 and passim) and Robinson (1891 and passim) saw a welcome decline in the number of described infraspecific taxa associated with the species they described from Mexico. However the new century did not bring a marked improvement in species delimitation. Urban (1902–3 and passim) and Standley (1924 and passim) between them described over 50 new species of Ipomoea, of which only a quarter are recognized today (Wood 2017.
From the mid-20^th century onwards, the situation has improved, partly as the result of the outstanding achievement of the Argentinian botanist Carlos O’Donell (1941, 1948a, 1948b, 1950a, 1950b, 1950c, 1952, 1953a, 1953b, 1959a, 1959b, 1959c, 1960). He described 56 species of Ipomoea of which 45 are accepted today, a success rate far higher than that of any of his predecessors (Wood 2017). Almost everything he described from Argentina is still accepted. He did much to rationalize the chaos left by Hassler, sorted out the Quamoclit Clade throughout the Americas and added significantly to our knowledge of Ipomoea in Bolivia, Peru and Brazil. The vast majority of his taxonomic decisions stand today and his judgement in an era before the internet is remarkable.
After O’Donell’s premature death in 1954, there has been a slow but steady increment of new species from the Americas. Isolated species from different countries have been published by various authors but the contributions of Dan Austin and Andy McDonald are the most significant. Accounts of Ipomoea in Panama, Ecuador, Venezuela by Austin (1976, 1982a, 1982b) have provided a framework for the study of Ipomoea in these countries. McDonald (1987a, 1995, 2001) has revised several groups of Ipomoea principally from Mexico but has also contributed with Austin and Murguía-Sánchez to the account in the Flora Mesoamerica (Austin et al. 2012). Other important contributions have been made by Carranza (1998 and passim) on Mexican Ipomoea and Liogier (1955 and passim) on those of Cuba and Hispaniola.