Pourthiaea (Rosaceae) - A common tree in New Jersey without an identification

General
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Dear iNaturalist community -

We need help to ID a common non-native tree naturalized throughout Princeton, NJ. The tree grows in the Herrontown Woods Arboretum and has been featured in several posts in iNaturalist. This unidentified Pourthiaea was also featured in a blog post by Stephen Hiltner (Princeton Nature Notes). Several posts are listed below.

Please note that we (Stephen Hiltner & John Clark) are confident this is NOT Pourthiaea villosa. P. villosa and the mystery Pourthiaea grow in the same forests, but they are vegetatively different (cf., notes and links below).

iNaturalist observations of Pourthiaea sp. indet. HERE:
https://www.inaturalist.org/observations/117251042
https://www.inaturalist.org/observations/117500236

Stephen Hiltner’s Princeton Nature Notes blog post HERE:
https://www.princetonnaturenotes.org/2022/01/a-mystery-tree-in-princeton.html

iNaturalist observations of Pourthiaea villosa HERE:
https://www.inaturalist.org/observations/117251045
https://www.inaturalist.org/observations/117795010

Liu and Hong (2016 – cf., citation below) concluded that Pourthiaea villosa should be broadly circumscribed. They wrote, “variations are continuous or with no statistical support, and there is no correlation between the different characters. Therefore, the characters used in this complex are of little value for species delimitation. As a result of our study, only one species, P. villosa, is recognized, without subdivision. Fourteen names are reduced as new synonyms of P. villosa… . “

It’s likely that Liu and Hong (2016) are referring to 14 heterotypic synonyms. If you consider homotypic synonyms (cf. POWO), then the list includes 40+ synonyms.

Interestingly, Liu & Hong (2016) did not consider P. lucida as conspecific with P. villosa (cf., note below).

“Pourthiaea lucida was reduced to a synonym of Photonia variabilis. Pourthiaea lucida have compound corymbose inflorescences and conspicuously impressed leaf veins.”

Are there any active taxonomists with expertise in Pourthiaea? Stephen Spongberg (author of Rosaceae for Flora of China) died in 2021. The other author of Pourthiaea for the Flora of China is Ling-ti Lu, who was born in 1930. I could not locate a current institutional address or email for Ling-ti Lu. I reached out to Dr. Hong (citation below), and he responded to my email, but said that he had retired and could not help with the ID (he is 85 years old). I have specimens, but I don’t know where to send them. Who else can we ask?

Liu, B. and D. Hong. 2016. A taxonomic revision of the Pourthiaea villosa complex (Rosaceae). Phytotaxa 244(3) 201-247.
http://dx.doi.org/10.11646/phytotaxa.244.3.1

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The Flora of North America treatment for the Rosaceae has been done, and can be accessed online. You might try getting in touch with some of the botanists who worked on that.

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Dear M_whitson -

Thank you for the suggestion! I reached out to Guy L. Nesom (author of Photinia for FNA) and Torsten Eriksson (systematist with expertise in Rosaceae).

Are Pourthiaea and Photinia conspecific? If not, does anyone know the generic characters that differentiate Pourthiaea and Photinia?

Thanks!
John

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Update: I received a response from Bin-Bin Liu, a molecular systematist who works on the genomics of Pourthiaea and Photinia (cf. citations below).

The mystery tree (Pourthiaea “lucida”) belongs in Pourthiaea. Outlined below are two useful generic characters provided by Dr. Bin-Bin Liu. Likewise, there are two generic characters that I cannot verify.

  1. Deciduous leaves

  2. Warty peduncles and pedicels (evident in the citation below)

https://www.inaturalist.org/observations/119710982

  1. Kribs’III–I heterogeneous rays in the wood [JLC - not familiar with this character]

  2. clusters of stone cells surrounded by parenchymatous cells in the flesh of pomes [JLC - will photograph fruits in the fall]

Conclusion: The mystery tree belongs in Pourthiaea because the leaves are deciduous and because of the presence of warts on the peduncles and pedicels.

Dr. Liu has not yet confirmed the ID, but he will visit Princeton, NJ, during his next trip to the USA. Likewise, he will incorporate tissue samples from our area (Princeton, NJ) into his ongoing genomic studies.

One more note: the proximity of P. villosa and P. “lucida” is interesting - they grow side-by-side in two areas in Princeton, NJ. They flower at different times (P. “lucida” flowers earlier and P. villosa flowers later).

Liu B-B, Hong D-Y, Zhou SL, Xu C, Dong WP, Johnson G, Wen J. 2019. Phylogenomic analyses of the photinia complex support the recognition of a new genus phippsiomeles and the resurrection of a redefined stranvaesia in maleae (rosaceae). Journal of Systematics and Evolution 57: 678-694.

Liu B-B, Campbell CS, Hong D-Y, Wen J. 2020a. Phylogenetic relationships and chloroplast capture in the amelanchier-malacomeles-peraphyllum clade (maleae, rosaceae): Evidence from chloroplast genome and nuclear ribosomal DNA data using genome skimming. Molecular phylogenetics and evolution 147: 106784.

Liu B-B, Liu G-N, Hong D-Y, Wen J. 2020b. Eriobotrya belongs to rhaphiolepis (maleae, rosaceae): Evidence from chloroplast genome and nuclear ribosomal DNA data. Frontiers in plant science 10: 1731.

Liu B-B, Ren C, Kwak M, Hodel RGJ, Xu C, He J, Zhou WB, Huang CH, Ma H, Qian GZ, Hong DY, Wen J. 2022. Phylogenomic conflict analyses in the apple genus malus s.L. Reveal widespread hybridization and allopolyploidy driving diversification, with insights into the complex biogeographic history in the northern hemisphere. Journal of integrative plant biology 64: 1020-1043.

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We did know this already (that they’re Pourthiaea) for what it’s worth. But great that he will make a special trip for it.

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Hi John–as a non-native genus (of however many species), do you know anything about the history of its naturalization? Was it introduced as a cultivated ornamental, or accidentally? Any idea how long ago? Depending on how long it has been naturalized, you might be able to find information in older flora treatments for the area, or even in the horticultural literature.

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Dear John (DCTropics),

I am not aware of any records on the introduction of Pourthiaea lucida in the USA. There are no iNaturalist observations of Pourthiaea “lucida” outside of Taiwan.

There is only one herbarium specimen of Photinia lucida (basionym = Pourthiaea lucida) at the Smithsonian (US). The collection is from the former Republic of Formosa (=Taiwan) from 1936 (cf., link below).

https://ids.si.edu/ids/media_view?id=ark:/65665/m3919aa14f75bc406eb0059b4b8e3e03f0&defaultView=image_dynamic

Best,
John

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