Little was done with Philodendron following Schott's death in 1865 until Adolf Engler, working at the Munich Botanical Garden (and later at the Berlin Botanical Garden), began his revisionary work on the Araceae. Schott had laid the groundwork, describing most of the genera that still exist today but he was dealing with only a small portion of the species. Taking up his first position at Munich in 1871, at age 27, Engler worked with various tropical families on the "Flora Brasiliensis" project publishing and working on a general review of the vegetative and floral morphology for the entire family (1877). Later in his powerful position as Director of the Berlin Botanical Garden, Engler would command attention and a wealth of herbarium specimens and living material from all over the world during Germany's preeminent period of domination in the botanical world preceding World War II. Since Engler was only 21 years of age at the time of Schott's death, it is not likely that the two ever met, but Engler would have had access to some of the same material, including living material from the Schönbrun greenhouses as well as Schott's notes and illustrations made over a 40 year period (Engler, 1876). Unlike modern workers he had access to Schott's herbarium in Vienna before it was destroyed during World War II. This is important for a continuum of species concepts in groups often described from inadequate material of unknown origin and worse yet sometimes lost all together by the action of the war.
Engler's treatment of the Araceae in Martius' Flora Brasiliensis (Engler, 1878) contained 116 species of Philodendron, 95 of which were members of P. sect. Philodendron (13 were in P. sect. Pteromischum and 8 in P. sect. Meconostigma). Only 47 species of Philodendron were actually known from Brazil. The work also included sectional and species descriptions as well as a key to all existing species of Philodendron. In this work Engler modified Schott's system of classification for Philodendron by recasting Schott's 'greges' as sections and reducing the number from 22 to 10. He also synonymized a number of species, reducing the total from 132 to 116 species. Only a single Central American species, P. oxycardium (= P. hederaceum ssp. oxycardium) was reported for Brazil, a fairly accurate picture as we know today. Only a few other species, namely P. fragrantissimum and P. verrucosum have been found to range into the Amazon drainage of South America. Two additional species, P. glanduliferum Matuda and P. brevispathum, have a subspecies or variety that occurs in the Amazon basin of South America but the same do not occur in Central America.
In the following year Adolph Engler's treatment of Philodendron for A. & C. de Candolle's "Monographie Phanerogamarum" (Engler, 1879) was essentially unchanged, adding only three additional species to bring the total to 120 species. Of these 93 species were members of P. subg. Philodendron and 20 of the epithets represented species currently known from Central America (now reduced to 15 through synonymy).
The final revisionary efforts by Engler on Philodendron published 20 years later (Engler, 1899) was changed only slightly at the subgeneric level from the 1878 work. One section was raised to subgeneric status and the remaining nine sections were included in P. subg. Philodendron (now P. subg. Philodendron). Despite minor changes made by Krause (1913), it is essentially Engler's classification that persists almost a century later. Engler's 1899 revision was substantially larger than Schott's last revision. Engler's revision contained 167 species, 134 of them in P. subg. Philodendron with 23 reported for Central America (reduced to 15 species through synonymy in this revision). One species, P. purpureoviride Engl., reported for Ecuador, is now known for Central America.
The species included in Engler's 1899 revision (Engler, 1899) in each section of P. subg. Euphilodendron in his revision for Central American are listed below:
P. sect. Pteromischum Schott: P. aurantiifolium (as synonym of P. guttiferum Kunth), P. guatemalense Engl., P. inaequilaterum, P. seguine, P. talamancae Engl.
P. sect. Baursia Reichb: P. wendlandii Schott
P. sect. Polyspermium Engl.
`gruppe' Platypodium Schott: P. pterotum
P. sect. Oligospermium Engl.`gruppe' Achyropodium Schott: P. verrucosum
`gruppe' Belocardium Schott: P. ligulatum Schott, P. immixtum Schott, P. advena, P. subovatum Schott (= P. advena), P. smithii Engl.
`gruppe' Oligocarpidium Engl.: P. pittieri Engl. (= P. hederaceum)
P. sect. Schizophyllum Schott: no species represented
P. sect. Polytomium Schott:
P. augustinum K. Koch (= P. radiatum),
P. radiatum Schott, P. warszewiczii K. Koch & Bouché
P. sect. Macrolonchium Schott: P. fragrantissimum
P. sect. Macrogynium Engl.:
P. hoffmannii Schott sensu Engl. (= P. jacquinii Schott)
The turn of the century saw major activity with Philodendron, no doubt due to Engler's just published revision. Engler made no changes in his revision but went on to publish 26 additional species (Engler, 1905). In addition, seven species were described by Alfred Barton Rendle, Ignatz Urban, Ambroise Gentil and N. E. Brown between 1901 and 1908.