| Shirleya | |
|---|---|
 | |
| Shirleya grahamae fruit | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Myrtales |
| Family: | Lythraceae |
| Genus: | †Shirleya Pigg & DeVore |
| Species: | †S. grahamae |
| Binomial name | |
| †Shirleya grahamae Pigg & DeVore | |
Shirleya is anextinctgenus in thecrape myrtle family,Lythraceae, which contains a single species,Shirleya grahamae. The genus and species are known fromMiddle Miocenefossils found in CentralWashington.
The species was first described from specimens ofsilicifiedfruits preserved inchert of the "Yakima Canyon Flora".[1] The chert was recovered from thetype locality "Hi hole" site, one of the "county line hole" fossil localities of the "Yakima Canyon Flora" located north ofInterstate 82 inYakima County, Washington.[2][1] The "Hi hole" site works strata was formerly thought to be part of the Museum Flow Package within the interbeds of the Sentinel Bluffs Unit of the central Columbia Plateau N2Grande Ronde Basalt,Columbia River Basalt Group. The Museum Flow Package interbeds are dated to themiddle Miocene and are approximately 15.6 million years old.[3] Later re-evaluation of the "Hi hole" site indicated that the site is included into a basalt flow, having deposited into pockets and crevasses on the surface of the flow, rather than being part of the interbedded Museum flow package.[1] The evaluation suggested the basalt is part of theWanapum Basalt and that the fossils are possibly a little younger than formerly reported.[2][1] Dating reported in 2007 of a related site nearEllensburg, Washington confirmed that the deposits worked are pockets within the basalt flows, and the 15.6 million year old date was accurate.[4]
At the time of study, theholotype fruit, specimen UWBM 55134, and a series of paratype specimens were preserved in theBurke Museum of Natural History and Culture while additional paratypes, and examined fossils that were not part of the type series, were part of the paleobotanical collections atArizona State University. The specimens represent a range of preservation conditions, ranging from exposed on weathered surfaces of the chert, totally weathered out of the chert, and as fully enclosed fruits in chert. A total of over 24 specimens in or preserved by chert were studied bypaleobotanists Kathleen Pigg and Melanie DeVore, with their 2005type description being published in theAmerican Journal of Botany. Pigg and DeVore coined the genus nameShirleya and thespecific epithetgrahamae as amatronym honoring Shirley A. Graham, then of theMissouri Botanical Garden inSt. Louis, Missouri for her work and "significant contributions" to the family Lythraceae.[1]
Based on similarities to the living genusLagerstroemia, Pigg and DeVore placedShirleya into Lythraceae, with no indication of a subfamily assignment. WhileShirleya has a number of features that are similar toLagerstroemia, there are also several distinct features. The fruits have a thickerpericarp that is similar to the generaDuabanga andSonneratia which have berry-like fruits, butShirleya fruits weredehiscent, unlike the berry-like fruits, as indicated by several isolated silicified fruit valves. The seeds inShirleya fruits develop near the tops of the fruitgynoecium with wings extending down towards the gynoecium base, while inLagerstroemia the seeds develop in reverse position, with the wing extending from the seed towards the top of the gynoecium.[1] These differences lead Pigg and DeVore to place the fossils in a new genus.[1]
The fruits ofShirleya range up to 10.0 mm (0.39 in) long and have a diameter of up to 12.5 mm (0.49 in) giving a subglobose outline. The central axis of the fruit is mostly aparenchymatouspith that forms a star shape. The fruits have between five and sevenwedge shapedlocules or minute chambers surrounding the central axis and narrowdehiscence slits which split on maturity, breaking the fruit into sections of two locule halves and the joining septum.[1] Each locule contains between five and seven mature seeds plus occasional smaller seeds.[1] The seeds are tightly packed into each locule and hang down from the apical area of the locule with wings curving out from the axis. The seeds are up to 4.6 mm (0.18 in) in length with a tail or hook on both theproximal and distal ends, and a wing that make up approximately two-thirds of the seed length. The seed wings each have a central bilobed parenchymatous mass that surroundsa central cavity.[1]