Editing Lumpers and splitters (section)

===Biology===
{{anchor|Lumping and splitting in biology}}
{{main|Taxonomy (biology)}}
The categorization and naming of a particular species should be regarded as a ''hypothesis'' about the [[evolution]]ary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be confirmed or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual [[organism]]s later identified as the same species. When two named species are agreed to be of the same species, the older species name is almost always retained dropping the newer species name honoring a convention known as "priority of nomenclature". This form of lumping is technically called synonymization. Dividing a taxon into multiple, often new, taxa is called splitting. Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognizing differences or commonalities between organisms.

For example, the number of [[genera]] used in [[Pteridophyte Phylogeny Group]] (PPG) I has proved controversial. PPG I uses 18 [[lycophyte]] and 319 [[fern]] genera.<ref name=PPGI>{{citation |author=PPG I |year=2016 |title=A community-derived classification for extant lycophytes and ferns |journal=Journal of Systematics and Evolution |volume=54 |issue=6 |pages=563–603 |doi=10.1111/jse.12229|doi-access=free}}</ref>  The earlier system put forward by Smith et al. (2006) had suggested a range of 274 to 312 genera for ferns alone.<ref name=SmitPryeSchuKora06>{{Citation |last1=Smith |first1=Alan R. |last2=Pryer |first2=Kathleen M. |last3=Schuettpelz |first3=Eric |last4=Korall |first4=Petra |last5=Schneider |first5=Harald |last6=Wolf |first6=Paul G. |date=2006 |title=A Classification for Extant Ferns |journal=Taxon |volume=55 |issue=3 |pages=705–731 |doi=10.2307/25065646 |jstor=25065646 |name-list-style=amp}}</ref> By contrast, the system of Christenhusz & Chase (2014) used 5 lycophyte and about 212 fern genera.<ref name=ChriChas14>{{Citation |last1=Christenhusz |first1=Maarten J. M. |last2=Chase |first2=Mark W. |date=2014 |title=Trends and concepts in fern classification |journal=Annals of Botany |volume=113 |issue=4 |pages=571–594 |doi=10.1093/aob/mct299 |pmid=24532607 |name-list-style=amp |doi-access=free |pmc=3936591}}</ref> The number of fern genera was further reduced to 207 in a subsequent publication.<ref name=ChriChas18>{{Citation |last1=Christenhusz |first1=Maarten J. M. |last2=Chase |first2=Mark W. |date=2018 |title=PPG recognises too many fern genera |journal=Taxon |volume=67 |issue=3 |pages=481–487 |doi=10.12705/673.2 |name-list-style=amp |doi-access=free}}</ref> Defending PPG I, Schuettpelz et al. (2018) argue that the larger number of genera is a result of "the gradual accumulation of new collections and new data" and hence "a greater appreciation of fern diversity and [..] an improved ability to distinguish taxa". They also argue that the number of species per genus in the PPG I system is already higher than in other groups of organisms (about 33 species per genus for ferns as opposed to about 22 species per genus for [[flowering plant|angiosperms]]) and that reducing the number of genera as Christenhusz and Chase propose yields the excessive number of about 50 species per genus for ferns.<ref name=SchuRouhPryeRoth18>{{Citation |last1=Schuettpelz |first1=Eric |last2=Rouhan |first2=Germinal |last3=Pryer |first3=Kathleen M. |last4=Rothfels |first4=Carl J. |last5=Prado |first5=Jefferson |last6=Sundue |first6=Michael A. |last7=Windham |first7=Michael D. |last8=Moran |first8=Robbin C. |last9=Smith |first9=Alan R. |date=2018 |title=Are there too many fern genera? |journal=Taxon |volume=67 |issue=3 |pages=473–480 |doi=10.12705/673.1 |name-list-style=amp |doi-access=free}}</ref> In response, Christenhusz & Chase (2018) argue that the excessive splitting of genera destabilises the usage of names and will lead to greater instability in future, and that the highly split genera have few if any characters that can be used to recognize them, making identification difficult, even to generic level. They further argue that comparing numbers of species per genus in different groups is "fundamentally meaningless".<ref name=ChriChas18/>