Dear Jeremy;
Bottom line:
Whether Lemnoids have a singleflower or a composed inflorescence cannot be determined at this point.
Details:
Traditionally =E2=80=9CLemnaceae=E2=80=9D havebeen interpreted as having an inflorescence. I emphasize here=E2=80=9Dinterpretation=E2=80=9D, and the extremely reduced Wolffia is not the right startingpoint for a comparison with Amphophallus.
One reason for theinflorescence interpretation is the un-equal development of stamens in Lemnaand Spirodela: Stamen-carpel-Stamen. This sequence is unusualfor flowers, where the organs of one identity tend to develop together, but notunusual for inflorescences, if each organ (or a group of not more than two) isconsidered a strongly reduced flower. The other reason is justtradition =E2=80=93 or burden =E2=80=93 from the past, when Lemoids were compared with Pistia(which is now rejected, see below).
HOWEVER:
1) Blurred Distinction:
Buzgo & Endress (2000) andBuzgo (2001) described that strong unidirectional development of flowerscan lead to a mixed up sequence of flower organ development; particularly inreduced inflorescences. Buzgo et al (2006) described that the distinctionof meristem identity of flower and inflorescence can be blurred in reducedflowers, and the debate whether reduced structures represent a flower or inflorescence is not serving anybody.
2) Phylogeny and AncestralCharacter States:
Looking at the molecularphylogeny of Araceae (Cabrera et al. 2008), we see that the Lemnoideae cladeinserts at the second node of the grade of basal Araceae, between the basalmost node to the sister clade with Orontioideae and Gymnostachys, and the thirdnode to Pothoideae (+Anthurium) and Monsteroideae. That is, Lemnoideaeare =E2=80=9Csurrounded=E2=80=9D by clades with bisexual and pethal-bearing flowers! Itis plausible that the ancestor of all Lemnoideae also had bisexual,petal-bearing flowers. It is not necessary (not parsimonious) toassume that the structures in Lemanoideae represent several distinct flowers.
3) The Pistia Legacy
The reason for sticking withthe interpretation of Lemnoid reproductive structures as inflorescence is a legacyor burden from the past, when Pistia was often proposed to be related toLemnoids (Engler, Stockey et al. 1997). This relation of Pistia toLemnoids has been rejected now several times (rev. Cabrera et al. 2008; alsoRenner et al. 2004), and no longer bears significance for the interpretation ofthe flower in Lemnoids. Just drop it!
As a conclusion, the structuremay well represent a single flower, possibly as the result of a stronglyreduced inflorescence (point 1 above), with the tubular membrane in somerepresenting a bract (spathe) or a perianth organ (since it lacks an axillarymeristem, =E2=80=9Cperianth=E2=80=9D would be appropriate).
Below some Literature =E2=80=93 I hopethis helps.
Matyas
Matyas Buzgo, PhD
Dept. of Biological Sciences,LSUS
One University Place
Shreveport, LA 71115, USA
(318) 797 5120 office
(318) 797 5222 fax
Literature
+ Arber, A. 1919. Thevegetative morphology of Pistia and the Lemnaceae. Proc. Roy. Soc. London 91 B:96-103
+ Bogner, J. 2000. FriedrichHegelmaier (1833-1906) and the Lemnaceae. Aroideana 23: 4-8
+ Buzgo, M. 1994. Inflorescencedevelopment of Pistia stratiotes (Araceae). Bot. Jahrb. Syst. 115 (4): 557-570
+ Buzgo, M., Endress, P.K.2000. Floral structure and development of Acoraceae and its systematic relationshipswith basal angiosperms. Int. J. Plant Sci. 161 (1): 23-41
+ Buzgo, M. 2001. Flowerstructure and development of Araceae compared with alismatids and Acoraceae. Bot. J. Linn. Soc. 136 (4):393-425
+ Buzgo, M. Soltis,D.E., Soltis, P.S., Kim, S., Ma, H., Hauser, B.A., Leebens-Mack, J. Johansen,B. 2006. Perianthdevelopment in the basal monocot Triglochin maritima (Juncaginaceae). - In:Columbus, J.T., Friar, E.A., Porter, J.M., Prince, L.M., Simpson, M.G. (eds),Monocots: Comparative Biology and Evolution, (excluding Poales). ALISO 22:107-125 (Claremont, CA, USA: Rancho Santa Ana Botanic Garden, ISSN:0065-6275)
+ Cabrera, L.I., Salazar, G.A.,Chase, M.W., Mayo S.J., Bogner, J., Davila, P. 2008 Phylogenetic Relationshipsof Aroids and Duckweeds (Araceae) inferred from coding and non-coding plastidDNA. Am. J. Bot. 95 (9): 1153-1165
+ Caldwell, O.W. 1899. On thelife-history of Lemna minor. Bot. Gaz. 27: 37-66
+ Landolt, E. 1980a.Biosystematische Untersuchungen in der Familie der Wasserlinsen (Lemnaceae). Ver=C3=B6ff. Geobot. Inst. ETH R=C3=BCbel 70 (1):5-247
+ Landolt, E. 1980b.Biosystematic investigations in the family of duckweeds (Lemnaceae), vol2. Thefamily of Lemnaceae - A monographic study. Ver=C3=B6ff. Geobot. Inst. ETH R=C3=BCbel 71:7-566
+ Landolt, E. 1986. The familyof Lemnaceae - a monographic study. Vol. 1 of the monograph: Morphology,karyology; ecology; geographic distribution; systematic position; nomenclature;descriptions. Ver=C3=B6ff. Geobot. Inst. ETH R=C3=BCbel 71 (2): ??
+ Landolt, E. Kandeler, R. 1987.Biosystematic investigations in the family of duckweeds (Lemnaceae), vol. 4.The family of Lemnaceae - A monographic study. Ver=C3=B6ff. Geobot. Inst. ETH R=C3=BCbel 95 (1):9-638
+ Renner, S.S., Zhang,L.-B. 2004. Biogeography ofthe Pistia clade (Araceae): Based on chloroplast and mitochondrial DNAsequences and Bayesian divergence time inference. Syst. Biol. 53 (3): 422-432
+ Stockey, R.A., Hoffman, G.L.,Rothwell, G.W. 1997 The fossil monocot Limnobiophyllum scutatum: Resolving thephylogeny of Lemnaceae. Am. J. Bot. 84 (3): 355-368
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