Re: If Wolffia is Araceae....

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Dear Jeremy;

 

Bottom line:

Whether Lemnoids have a single flower or a composed inflorescence cannot be determined at this point.

 

Details:

Traditionally “Lemnaceae” have been interpreted as having an inflorescence.  I emphasize here ”interpretation”, and the extremely reduced Wolffia is not the right starting point for a comparison with Amphophallus. 

 

One reason for the inflorescence interpretation is the un-equal development of stamens in Lemna and Spirodela:  Stamen-carpel-Stamen.  This sequence  is unusual for flowers, where the organs of one identity tend to develop together, but not unusual for inflorescences, if each organ (or a group of not more than two) is considered a strongly reduced flower.   The other reason is just tradition – or burden – from the past, when Lemoids were compared with Pistia (which is now rejected, see below).

 

HOWEVER:

1) Blurred Distinction:

Buzgo & Endress (2000) and Buzgo (2001)  described that strong unidirectional development of flowers can lead to a mixed up sequence of flower organ development; particularly in reduced inflorescences.  Buzgo et al (2006) described that the distinction of meristem identity of flower and inflorescence can be blurred in reduced flowers, and the debate whether reduced structures 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 grade of basal Araceae, between the basal most node to the sister clade with Orontioideae and Gymnostachys, and the third node to Pothoideae (+Anthurium) and Monsteroideae.  That is, Lemnoideae are “surrounded” by clades with bisexual and pethal-bearing flowers!  It is plausible that the ancestor of all Lemnoideae also had bisexual, petal-bearing flowers.  It is not necessary (not parsimonious) to assume that the structures in Lemanoideae represent several distinct flowers.

 

3) The Pistia Legacy

The reason for sticking with the interpretation of Lemnoid reproductive 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 bears significance for the interpretation of the flower in Lemnoids.  Just drop it!

 

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 perianth organ (since it lacks an axillary meristem, “perianth” would be appropriate).

 

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 the Lemnaceae. Proc. Roy. Soc. London 91 B: 96-103

+ Bogner, J. 2000. Friedrich Hegelmaier (1833-1906) and the Lemnaceae. 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 and development of Acoraceae and its systematic relationships with basal angiosperms. Int. J. Plant Sci. 161 (1): 23-41

+ Buzgo, M. 2001. Flower structure 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. Perianth development 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 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 der Familie der Wasserlinsen (Lemnaceae). Veröff. Geobot. Inst. ETH Rübel 70 (1): 5-247

+ Landolt, E. 1980b. Biosystematic investigations in the family of 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 monographic study. Vol. 1 of the monograph: Morphology, karyology; ecology; geographic distribution; systematic position; nomenclature; descriptions. Veröff. Geobot. Inst. ETH Rübel 71 (2): ??

+ Landolt, E. Kandeler, R. 1987. Biosystematic investigations in the family of duckweeds (Lemnaceae), vol. 4. The family of Lemnaceae - A monographic study. Veröff. Geobot. Inst. ETH Rübel 95 (1): 9-638

+ Renner, S.S., Zhang, L.-B. 2004. Biogeography of the Pistia clade (Araceae): Based on chloroplast and mitochondrial DNA sequences 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 the phylogeny of Lemnaceae. Am. J. Bot. 84 (3):  355-368

 

 

 

 

 

 

Hello Aroid-L Listers,

Without wanting to open a proverbial can of worms (which may have never really been closed...), I do have a question about Wolffia, it's flower structure and thus its' (current?) inclusion in Araceae.

I'll give the reason for my question first, which leads to the actual query itself - we have many aroids on public display here at the RBG Melbourne, and for a long time I've wanted to interpret to our visitors that they can stand under the plant with the world's largest inflorescence (The fabulous Amorphophallus titanum of course) while trying to spot the world's smallest flowering plant 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 smallest flower" beside the inclusion of Wolffia in Araceae, which as I understand it, is renowned for its' spathe/spadix inflorescence - having tried to stumble my way through much taxonomic jargon (of which my understanding is regrettably rather poor) I'm still none the wiser, and so we arrive at my point of query...

Does Wolffia have a single flower or an inflorescence? Seeing that in clear print makes me realise just how limited my understanding may be as I'm sure I can hear echoes of "it's not that simple" bouncing back already! I have 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 be educated...

Jeremy P
RBG Melbourne