AROID CLASSIFICATION

686
Annals of the
Missouri Botanical Garden
some numbers (x = 14 in Pistia, x = 1 1 in Ambrosina), and pollen nuclear numbers (III in Pistia,
II in Ambrosina). Thus, though these genera are
here considered closely related, they are maintained in separate tribes.
Pistia and Ambrosina show more similarities to
as visualized as a result of the present investigations, pairs the Pothoideae and Philodendroideae,
on one hand, against the Lasioideae and Aroideae,
on the other. The former group consists of fundamentally rhizomatous or scandent plants with
basically distichous leaves, a base chromosome
number possibly other than x = 7 or 14 (x = 12?),
and a largely Gondwanalandic distribution. The
latter group consists of fundamentally rhizomatous
or tuberous plants with basically spiral phyllotaxy,
a base chromosome number of x = 7 or 14, and
a basically Laurasian distribution. The position of
Colocasioideae relative to these two groups remains
unclear. Explanations for the two secondary diand Lachotomies, Pothoideae/Philodendroideae
are found under the headings
sioideae/Aroideae,
"Homalomeniae,
etc." and "Thomsonieae," respectively. Tertiary and lower-level dichotomies are
discussed under the appropriate headings.
I consider the following aspects of Figure 1 to
be particularly tentative: the position of Colocasioideae (which may even be diphyletic); the derivation of Zamioculcadeae, an isolated group of
obscure affinity; the position of Spathicarpeae within Philodendroideae (this tribe may be more cladistically primitive than indicated); and the composition of the subfamily Lasioideae, the members
of which are associated mainly on the basis of
symplesiomorphies. The cladistic relationship among
the various "alliances" of subfamily Philodendroideae is highly speculative, as is the composition of
some of these groups (particularly the "Aglaonema
alliance").
Ariopsis than to Arisarum. In fact, Pistia shares
more putative apomorphies with Ariopsis than with
Ambrosina. These mostly pertain to a strong overall resemblance in inflorescence structure, gynoecial morphology, stamens, ovules, and base chromosome number. Ariopsis differs from Pistia,
Ambrosina, and the Cryptocoryninae in having
globose, spinose, starchless pollen, and hence has
been treated here as a sister group to both of those
taxa rather than to Pistia alone.
Arisarum differs from Pistia and Ambrosina in
several important respects: spathe free from the
spadix, a nonstipitate male portion of the spadix,
possession of a sterile apical appendage, a single
stamen per male flower, several female flowers per
inflorescence, and transverse anther dehiscence.
The genus shows certain similarities to most of the
other taxa in Aroideae (especially Thomsonieae,
Arinae, and Ariopsis), but no compelling relationship to any one taxon. It is apparently quite isolated
and is here maintained in its own tribe.
It should be clear from the foregoing discussion
that, despite its peculiar aspect, Pistia is an integral
part of the subfamily Aroideae. It clearly cannot
be accorded separate subfamilial status since to do
so would render the Aroideae paraphyletic.
A BEGINNING
AROIDCLADISTICS:
A preliminary, quasi-cladistic model of the putative phylogenetic relationships of the important
infrafamilial taxa in Araceae appears in Figure 1.
This diagram was constructed in a piecemeal fashion, in a manner thought to best reflect the implications of the available data; it is not the product
of a rigorous, computer-mediated algorithm. This
subjective interpretation was necessary due to the
small amount of characters employed in the analysis compared with the number of taxa under consideration. Computer analysis of aroid cladistics can
be expected to provide valuable new insights, and
work toward that goal is currently underway in at
least two different laboratories. Meanwhile, highest
priority should be given to the search for new kinds
of systematically useful characters in Araceae, and
to the expansion of the data base (for these and
already established characters) to cover all genera
of the family.
The fundamental dichotomy in Araceae (Fig. 1),
AROID CLASSIFICATION:NEW AND OLD PERSPECTIVES
Inasmuch as aroid cladistics are still in the embryonic stage, the infrafamilial classification of Araceae is bound to remain in a state of flux. Thus,
the classification at the end of this section (Table
5) is necessarily tentative, as are all other existing
aroid classifications. Although there is a natural
impatience on the part of workers in the field for
a rigid and finalized system, our present comprehension of aroid phenetics falls far short of what
will be needed for the construction of the finely
resolved cladogram upon which such a classification must be based.
The linear order of the classification presented
here reflects the constraints of the cladogram (Fig.
1); no additional significance should be imputed to
the sequencing of taxa within larger groups. With
the exception of Philodendroideae, no paraphyletic
(according to the cladogram) groups have been
accepted; otherwise, no attempt has been made to
Volume 77, Number 4
1990
687
Grayum
Evolution and Phylogeny of Araceae
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roidea
Proposed cladogram for major aroid subtaxa.
rigidly apply the criteria of cladistic classification.
Since this classification is recognized as tentative,
an effort was made to maintain nomenclatural stability by accepting Englerian ranks. In a few cases
(particularly his tribes Colocasieae and Areae),
however, this was deemed inadvisable. No systematic effort was made to ensure that various taxa
at the same rank were equivalent in terms of their
"level of peculiarity," and new suprageneric taxa
have been described only where absolutely necessary.
The Araceae have here been grouped into five
subfamilies in light of the information organized in
the foregoing section. The system resulting from
this arrangement most closely resembles that of
Hotta (1970) in that Acorus has been removed
from Pothoideae; Pothoideae and Monsteroideae
are combined; and Calloideae are broken up (with
Calla assigned to the Philodendroideae and the
Orontieae to the Lasioideae, in both systems).
The present system differs from Hotta's mainly
in that Acorus has now been removed from the
Araceae altogether (Grayum, 1987), Pistia has
been inserted directly into the Aroideae, and the
Colocasioideae are here retained as a subfamily
(rather than submerged in Philodendroideae, as
Hotta has done). Hotta is probably at least partly
correct on the latter issue, however: it is perhaps
inevitable that at least part of the Colocasioideae
will ultimately have to be subsumed in Philodendroideae. I tentatively maintain the former subfamily, owing to a good deal of uncertainty over the
exact manner in which the two taxa are related,
and particularly to some lingering suspicion that
the Colocasioideae may in fact be diphyletic (see
under Colocasioideae).
Significant departures from the Englerian system below the subfamily level are as follows (the
rationales for all of these changes have been presented in previous sections): Heteropsis is moved
from the Potheae into the Monstereae; the Monstereae are here envisioned as being more closely
related to the Potheae than to the Spathiphylleae.
Culcasia is transferred out of Pothoideae into
688
TABLE 5.
Annals of the
Missouri Botanical Garden
A preliminary new classification of the Araceae (with nomenclature based on Nicolson, 1984b).
Family Araceae Juss.
I. Subfamily Pothoideae Engl.
1. Tribe Gymnostachydeae Nakai (Gymnostachys)
2. Tribe Spathiphylleae Engl. (Spathiphyllum, Holochlamys)
3. Tribe Anthurieae Engl. (Anthurium)
4. Tribe Potheae Engl. (Pothos, Pedicellarum, Pothoidium)
5. Tribe Anadendreae Bogner & J. French (Anadendrum)
6. Tribe Monstereae Engl.
a. Subtribe Heteropsidinae Engl. (Heteropsis)
b. Subtribe Monsterinae Schott (Rhaphidophora, Monstera, Amydrium, Epipremnum, Scindapsus,
Alloschemone, Stenospermation, Rhodospatha)
7. Tribe Zamioculcadeae Engl. (Zamioculcas, Gonatopus)
II. Subfamily Calloideae Schott
A. Calla Alliance
8. Tribe Calleae Schott (Calla)
B. Nephthytis Alliance
9. Tribe Nephthytideae Engl. (Nephthytis, Anchomanes, Pseudohydrosme)
10. Tribe Callopsideae Engl. (Callopsis, Ulearum, Filarum, Zomicarpella)
11. Tribe MontrichardieaeEngl. (Montrichardia)
C. Aglaonema Alliance
12. Tribe Anubiadeae Engl. (Anubias)
13. Tribe Zantedeschieae Engl. (Zantedeschia)
14. Tribe Aglaonemateae Engl. (Aglaonema, Aglaodorum)
15. Tribe Spathicarpeae Schott (Mangonia, Asterostigma, Synandrospadix, Taccarum, Gorgonidium,
Gearum, Spathantheum, Spathicarpa)
16. Tribe Dieffenbachieae Engl. (Dieffenbachia)
17. Tribe Bognereae Mayo & Nicolson (Bognera)
D. Peltandra Alliance
18. Tribe Peltandreae Engl. (Peltandra, Typhonodorum)
19. Tribe Arophyteae Bogner (Arophyton, Carlephyton, Colletogyne)
20. Tribe Schismatoglottideae Nakai (Schismatoglottis, Piptospatha, Bucephalandra, Phymatarum, Aridarum, Heteroaridarum, Hottarum)
E. Philodendron Alliance
21. Tribe Culcasieae Engl. (Culcasia)
22. Tribe Cercestideae Grayum' (Cercestis)
23. Tribe Homalomeneae (Schott) M. Hotta (Furtadoa, Homalomena)
24. Tribe Philodendreae Schott (Philodendron)
III. Subfamily Colocasioideae Engl.
25. Tribe Zomicarpeae Schott (Zomicarpa)
26. Tribe Colocasieae Engl.
a. Subtribe Protarinae (Engl.) Grayum' (Protarum)
b. Subtribe Steudnerinae Engl. & K. Krause (Steudnera)
c. Subtribe Remusatiinae Grayum' (Remusatia, Gonatanthus)
d. Subtribe Colocasiinae Schott (Colocasia, Alocasia)
27. Tribe Caladieae Schott
a. Subtribe Jasarinae Grayum' (Jasarum)
b. Subtribe Scaphispathinae Grayum' (Scaphispatha)
c. Subtribe Caladiinae Engl. & K. Krause (Caladium, Xanthosoma, Chlorospatha, Aphyllarum)
d. Subtribe Syngoniinae Schott (Syngonium)
e. Subtribe Hapalininae Engl. & K. Krause (Hapaline)
IV. Subfamily Lasioideae Engl.
28. Tribe Symplocarpeae Engl. (Symplocarpus, Lysichiton)
29. Tribe Orontieae R. Br. ex Dumort. (Orontium)
30. Tribe Lasieae Engl.
a. Subtribe Dracontiinae Schott (Cyrtosperma, Lasia, Anaphyllum, Podolasia, Urospatha, Dracontioides, Dracontium)
b. Subtribe Pycnospathinae Bogner (Pycnospatha)
31. Tribe Stylochaetoneae Schott (Stylochaeton)
Volume 77, Number 4
1990
TABLE 5.
Grayum
Evolution and Phylogeny of Araceae
689
Continued.
V. Subfamily Aroideae Engl.
32. Tribe Thomsonieae Blume (Pseudodracontium, Amorphophallus)
33. Tribe Arisareae Dumort. (Arisarum)
34. Tribe Pinellieae Nakai (Pinellia)
35. Tribe Pistieae Blume (Pistia)
36. Tribe Cryptocoryneae Blume (Cryptocoryne, Lagenandra)
37. Tribe Ambrosineae Schott (Ambrosina)
38. Tribe Ariopsideae Engl. (Ariopsis)
39. Tribe Arisaemateae Nakai (Arisaema)
40. Tribe Areae Engl. (Arum, Dracunculus, Helicodiceros, Theriophonum, Typhonium, Sauromatum,
Eminium, Biarum)
'Validation of new taxa and new combination:
Cercestideae Grayum, trib. nov. Philodendroidearum.
Plantae africanae praecipue scandentes canalibus laticiferis folia spiraliter disposita sine geniculo; antherae sine
endothecio pollen amylaceum continentes; radices sine hypodermate sclerotico canalibus resiniferis; x = 21.
Protarinae, stat. nov.; Protareae Engl., in Engler & Prantl, Nat. Pflanzenfam. Nachtr. 3: 29, 34 (1906).
Remusatiinae Grayum, subtrib. nov. Colocasiearum.
Plantae orbis antiqui polline globoso spinoso trinucleato; spadix sine appendice sterili apicali.
Jasarinae Grayum, subtrib. nov. Caladiearum.
Plantae aquaticae submersae rhizomatosae venezuelensium caulibus sine systemate vasculari corticali foliis linearolanceolatis; ovarium uniloculare placentatione basali ovulis 2; semina sine endospermio; exinium pollinis omnino
reticulatum; x = 1 1.
Scaphispathinae Grayum, subtrib. nov. Caladiearum.
Plantae brasiliensium sine floribus sterilibus ovariis unilocularibus placentatione basali; exinium pollinis verrucis
applanatis multangulis.
the Philodendroideae in the neighborhood of Philodendron; Cercestis is removed from the Nephthytideae to its own tribe, Cercestideae, while the
former tribe is enlarged to accommodate Anchomanes and Pseudohydrosme (formerly of the
Thomsonieae); Cercestideae, Nephthytideae, and
Montrichardieae are all transferred from Lasioideae to Philodendroideae; Peltandra and Typhonodorum are joined in a single tribe, the Peltandreae; the Callopsideae, Spathicarpeae, and
Arophyteae are also moved from Aroideae to Philodendroideae. The Zomicarpeae are broken up,
Zomicarpa being assigned to the Colocasioideae
(as a separate tribe) and the remaining three genera
to the Callopsideae (Philodendroideae). The lastmentioned subfamily,here much enlarged, has been
divided into five informal "alliances."
The internal classification of subfamily Colocasioideae is changed to reflect a basic dichotomy,
largely between New and Old World taxa. Protarum is transferred from the Aroideae into the
Old World tribe Colocasieae as a separate subtribe;
Steudnera is dissociated from Remusatia and Gonatanthus and is included in its own subtribe; the
latter two genera (which probablyought to be combined) are placed in a new subtribe, Remusatiinae;
Jasarum and Scaphispatha are each accorded
separate subtribal status in the New World tribe
Caladieae; Syngonium is included in this tribe as
the monotypic subtribeSyngonieae. The Old World
genus Hapaline agrees phenetically with the Caladieae and has been included there in its own
subtribe.
The Lasioideae are expanded to include Stylochaeton (transferred from Aroideae) and the tribe
Orontieae (sensu lato); the Thomsonieae, however,
are moved out of Lasioideae and into Aroideae;
Ariopsis is moved from the Colocasioideae into the
Aroideae.
The following departures from Engler's usage
(below the subfamily level) may be noted in the
present system: nine tribes or subtribes (Potheae,
Philodendreae, Nephthytideae, Colocasieae, Steudnerinae, Caladiinae, Orontieae, Thomsonieae,
Zomicarpeae, and Areae) were judged to be more
or less artificial, and variously disbanded;ten tribes
or subtribes underwent a change of rank (Heteropsideae to Heteropsidinae;Schismatoglottidinaeto
Schismatoglottideae; Homalomeninae to Homalomeneae; Protareae to Protarinae; Syngonieae to
Syngoniinae; Arisarinae to Arisareae; Atherurinae
to Pinellieae; Arisaematinae to Arisaemateae; Ambrosininae to Ambrosineae; and Cryptocoryninae
to Cryptocoryneae);subtribe Colocasiinae and tribe
Callopsideae were enlarged; five tribes or subtribes
(Acoreae, Typhonodoreae, Philodendrinae, Alo-
690
casiinae, and Arinae) were eliminated; and 10
Monsterinae,
Anadendreae,
(Gymnostachydeae,
Cercestideae, Bognereae, Remusatiinae, Jasarinae,
Scaphispathinae, Symplocarpeae, and Pistieae) were
added on.
Many of the changes in the accompanying classification (Table 5) represent a return to pre-Englerian concepts. Although Engler's contributions
revolutionized our understanding of aroid phenetics, I believe he made a fundamental and rather
grave error in unduly emphasizing often superficial
vegetative features (e.g., leaf venation and morphology) in constructing his classification. Engler's
treatment of the tribes Lasieae and Thomsonieae
provides a particularly glaring example of superficially convergent taxa juxtaposed on this basis;
his inclusion of the genera Anchomanes and Pseudohydrosme within the Thomsonieae constitutes a
somewhat less obvious case.
There are very good reasons why reproductive
characteristics of higher plants should be accorded
more taxonomic "weight" than vegetative features
(see, e.g., Stebbins, 1970). Any mutation or recombination event significantly affecting the reproductive organs (e.g., a change in style length,
petal color, timing of anther dehiscence or stigma
receptivity, pollen exine ornamentation, chromosome features, etc.) would be much more likely to
result in reproductive isolation, followed by speciation and a consequent cladistic dichotomy than
would an event of similar magnitude affecting only
vegetative organs. Therefore, within a given clade,
one should expect to encounter considerably more
variation in vegetative than in reproductive struchas long been intuitively appreciated by
tures-as
plant taxonomists. With regard to the Araceae,
this would suggest that the strikingly similar leaf
morphology of, say, Dracontium and Amorphophallus ought not to be emphasized so much as
their radically different floral and pollen morphologies.
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