Development of reproductive structures in the sole Indian species of Hydatellaceae, Trithuria konkanensis, and its morphological differences from Australian taxa
Dmitry D. Sokoloff A , Margarita V. Remizowa A , Shrirang R. Yadav B and Paula J. Rudall C DA Department of Higher Plants, Biological Faculty, Moscow State University, 119991 Moscow, Russia.
B Shivaji University, Vidyanagar, Kolhapur 416 004, India.
C Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3DS, UK.
D Corresponding author. Email: p.rudall@kew.org
Australian Systematic Botany 23(4) 217-228 https://doi.org/10.1071/SB10015
Submitted: 30 March 2010 Accepted: 21 May 2010 Published: 31 August 2010
Abstract
The current paper presents new morphological and developmental data on the sole Indian species of Hydatellaceae, T. konkanensis Yadav & Janarthanam, and explores its morphological differences from Australian members of the family. On the basis of morphology and ecology, T. konkanensis appears to be closely related to T. lanterna, a species from tropical northern Australia that resembles T. konkanensis more closely than does any other Australian taxon. However, fruits are dehiscent in T. lanterna and indehiscent in T. konkanensis. Developmental data on T. konkanensis are significant for interpreting the reproductive units in Hydatellaceae. In T. konkanensis, each reproductive unit consists of two bract-like phyllomes, several carpels and a single central stamen that is initiated before the carpels. The earliest-formed carpels are those closest to the stamen; the latest-formed carpels are closest to the phyllomes. Despite their apparently whorled arrangement, the phyllomes are initiated sequentially. The spatial arrangement of the earliest-initiated carpels makes it unlikely that the phyllomes subtend any axillary structures. So far, there is no robust direct evidence in favour of a multiaxial (pseudanthial) morphological interpretation of bisexual reproductive units of Hydatellaceae. No evidence for dichogamy is present in bisexual reproductive units of either Indian or Australian Hydatellaceae, a feature that contrasts with the common presence of protogyny in flowers of other early divergent extant angiosperms.
Additional keywords: flower, fruit, homology, Hydatellaceae, inflorescence, morphology, Nymphaeales, seed.
Acknowledgements
We are grateful to Richard Bateman, Terry Macfarlane and two anonymous reviewers for helpful discussion and comments. M. V. R. and D. D. S. acknowledge support from the President of Russia grant no. MD-2644.2009.4, RFBR grant no. 09-04-01155 and the Ministry of Education and Science of Russia.
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Appendix 1
Identification key of Trithuria species with bisexual reproductive units
1. Fruits lacking longitudinal ribs. Fruit surface with dense and well recognisable papillae ..........T. cowieana (N Australia)
Fruits with three longitudinal ribs. Fruit surface lacking papillae ..........2
2. Seeds smooth, covered by firm cuticle. Seedlings lacking a cotyledonary sheath, with cotyledon represented by a haustorium only ..........3
Mature seeds clearly sculptured, honeycombed when dry, with individual exotesta cells well recognisable from the surface. Seedlings possessing a bilobed cotyledonary sheath to which a haustorium is attached ..........4
3. Fruits indehiscent. Reproductive units always possessing two bract-like phyllomes. Longest stigmatic hairs longer than 3 mm ..........T. konkanensis (India)
Dry mature fruits dehiscing by separating three longitudinal ribs. Reproductive units possessing 2–4 bract-like phyllomes. Longest stigmatic hairs usually not exceeding 3 mm ..........T. lanterna (N Australia)
4. Reproductive units typically possessing four (rarely three or up to seven, very rarely two) acute or apiculate bract-like phyllomes. Reproductive units typically borne on distinct, often long peduncles. (Less frequently, reproductive units almost sessile, but such plants were not collected from Western Australia, where the next species occurs.) ..........T. submersa (SW, S and SE Australia, Tasmania)
Reproductive units possessing two (very rarely four) acuminate bract-like phyllomes. Reproductive units virtually sessile (or very rarely possessing long peduncles) ..........T. bibracteata (SW Australia)
