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2009/7/23 Buzgo, Matyas
Dear Jeremy;
Bottom line:
Whether Lemnoids have a single flower or a composedinflorescence cannot be determined at this point.
Details:
Traditionally “Lemnaceae” have been interpreted ashaving an inflorescence. I emphasize here ”interpretation”, and theextremely reduced Wolffia is not the right starting point for a comparison withAmphophallus.
One reason for the inflorescence interpretation is the un-equaldevelopment of stamens in Lemna and Spirodela: Stamen-carpel-Stamen. Thissequence is unusual for flowers, where the organs of one identity tend to developtogether, but not unusual for inflorescences, if each organ (or a group of notmore than two) is considered a strongly reduced flower. The other reason isjust tradition – or burden – from the past, when Lemoids werecompared with Pistia (which is now rejected, see below).
HOWEVER:
1) Blurred Distinction:
Buzgo & Endress (2000) and Buzgo (2001) described thatstrong unidirectional development of flowers can lead to a mixed up sequence offlower organ development; particularly in reduced inflorescences. Buzgo et al(2006) described that the distinction of meristem identity of flower andinflorescence can be blurred in reduced flowers, and the debate whether reducedstructures represent a flower or inflorescence is not serving anybody.
2) Phylogeny and Ancestral Character States:
Looking at the molecular phylogeny of Araceae (Cabrera et al.2008), we see that the Lemnoideae clade inserts at the second node of the gradeof basal Araceae, between the basal most node to the sister clade withOrontioideae and Gymnostachys, and the third node to Pothoideae (+Anthurium)and Monsteroideae. That is, Lemnoideae are “surrounded” by cladeswith bisexual and pethal-bearing flowers! It is plausible that the ancestorof all Lemnoideae also had bisexual, petal-bearing flowers. It is notnecessary (not parsimonious) to assume that the structures in Lemanoideaerepresent several distinct flowers.
3) The Pistia Legacy
The reason for sticking with the interpretation of Lemnoidreproductive structures as inflorescence is a legacy or burden from the past,when Pistia was often proposed to be related to Lemnoids (Engler, Stockey et al.1997). This relation of Pistia to Lemnoids has been rejected now several times(rev. Cabrera et al. 2008; also Renner et al. 2004), and no longer bearssignificance for the interpretation of the flower in Lemnoids. Just dropit!
As a conclusion, the structure may well represent a single flower,possibly as the result of a strongly reduced inflorescence (point 1 above),with the tubular membrane in some representing a bract (spathe) or a perianthorgan (since it lacks an axillary meristem, “perianth” would beappropriate).
Below some Literature – I hope this 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. The vegetative morphology of Pistia and theLemnaceae. Proc. Roy. Soc. London 91 B: 96-103
+ Bogner, J. 2000. Friedrich Hegelmaier (1833-1906) and theLemnaceae. Aroideana 23: 4-8
+ Buzgo, M. 1994. Inflorescence development of Pistia stratiotes(Araceae). Bot. Jahrb. Syst. 115 (4): 557-570
+ Buzgo, M., Endress, P.K. 2000. Floral structure anddevelopment of Acoraceae and its systematic relationships with basalangiosperms. Int. J. Plant Sci. 161 (1): 23-41
+ Buzgo, M. 2001. Flower structure and development of Araceaecompared 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. Perianth development in thebasal monocot Triglochin maritima (Juncaginaceae). - In: Columbus, J.T., Friar,E.A., Porter, J.M., Prince, L.M., Simpson, M.G. (eds), Monocots: ComparativeBiology 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 Relationships of Aroids and Duckweeds(Araceae) inferred from coding and non-coding plastid DNA. Am. J. Bot. 95 (9):1153-1165
+ Caldwell, O.W. 1899. On the life-history of Lemna minor. Bot.Gaz. 27: 37-66
+ Landolt, E. 1980a. Biosystematische Untersuchungen in derFamilie der Wasserlinsen (Lemnaceae). Veröff. Geobot. Inst. ETHRübel 70 (1): 5-247
+ Landolt, E. 1980b. Biosystematic investigations in the familyof duckweeds (Lemnaceae), vol2. The family of Lemnaceae - A monographic study.Veröff. Geobot. Inst. ETH Rübel 71: 7-566
+ Landolt, E. 1986. The family of Lemnaceae - a monographicstudy. Vol. 1 of the monograph: Morphology, karyology; ecology; geographicdistribution; systematic position; nomenclature; descriptions. Veröff. Geobot.Inst. ETH Rübel 71 (2): ??
+ Landolt, E. Kandeler, R. 1987. Biosystematic investigations inthe family of duckweeds (Lemnaceae), vol. 4. The family of Lemnaceae - Amonographic study. Veröff. Geobot. Inst. ETH Rübel 95 (1):9-638
+ Renner, S.S., Zhang, L.-B. 2004. Biogeographyof the 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 fossilmonocot Limnobiophyllum scutatum: Resolving the phylogeny of Lemnaceae. Am. J.Bot. 84 (3): 355-368
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From:aroid-l-bounces@gizmoworks.com [mailto:aroid-l-bounces@gizmoworks.com] OnBehalf Of Jeremy P
Sent: Sunday, July 19, 2009 7:25 PM
To: Discussion of aroids
Subject: [Aroid-l] If Wolffia is Araceae....
Hello Aroid-L Listers,
Without wanting to open a proverbial can of worms (which may have never reallybeen closed...), I do have a question about Wolffia, it's flower structure andthus its' (current?) inclusion in Araceae.
I'll give the reason for my question first, which leads to the actual queryitself - we have many aroids on public display here at the RBG Melbourne, andfor a long time I've wanted to interpret to our visitors that they can standunder the plant with the world's largest inflorescence (The fabulous Amorphophallustitanum of course) while trying to spot the world's smallest floweringplant floating on the pond... Wolffia.
So, my mind began ticking away at the finer details of how to tell the story,and became unsure when I put the statement "the world's smallestflower" beside the inclusion of Wolffia in Araceae, which as Iunderstand it, is renowned for its' spathe/spadix inflorescence - havingtried to stumble my way through much taxonomic jargon (of which myunderstanding is regrettably rather poor) I'm still none the wiser, and so wearrive at my point of query...
Does Wolffia have a single flower or an inflorescence? Seeing that in clearprint makes me realise just how limited my understanding may be as I'm sure Ican hear echoes of "it's not that simple" bouncing back already! Ihave come across mention of unisexual aroids flowers (on the IAS website,Genera page) but wasn't sure if that correlates to having an inflorescence...again a confession of my limited understanding.
So, with that all said I wait, with gratitude for any replies, to beeducated...
Jeremy P
RBG Melbourne
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