Architectural Pattern: Study of orchid architecture using tools to take quick measurements of virtual specimens
Authors: Gourraud Aurore , Vignes Lebbe Régine , Kerner Adeline , Pignal Marc 
Published: September 2021

The joint use of two tools applied to plant description, XPER3 and Recolnat Annotate, made it possible to study vegetative architectural patterns (Fig. 1) of the Dendrobium (Orchidaceae) in New Caledonia defined by N. Hallé (1977). This approach is not directly related to taxonomy, but to the definition of sets of species grouped according to a growth pattern.
In the course of this work, the characters stated by N. Hallé were analysed and eventually amended to produce a data matrix and generate an identification key.

Study materials: Dendrobium Sw. in New Caledonia

New Caledonia is an archipelago in the Pacific Ocean, a French overseas territory located east of Australia. It is one of the 36 biodiversity hotspots in the world.
The genus Dendrobium Sw. sensu lato is one of the largest in the family Orchidaceae and contains over 1220 species. In New Caledonia, it includes 46 species. In his revision of the family, N. Hallé (1977) defined 14 architectural groups, into which he divided the 31 species known at that time. These models are based on those defined by F. Hallé and Oldeman (1970). But they are clearly intended to group species together for identification purposes.

Architectural pattern:

A pattern is a set of vegetative or reproductive characters that define the general shape of an individual. Developed by mechanisms linked to the dominance of the terminal buds, the architectural groups are differentiated by the arrangement of the leaves, the position of the inflorescences or the shape of the stem (Fig. 1). Plants obeying a given pattern do not necessarily have phylogenetic relationships. These models have a useful application in the field for identifying groups of plants.
Monocotyledonous plants, and in particular the Orchidaceae, lend themselves well to this approach, which produces stable architectural patterns.

Recolnat Annotate

Recolnat Annotate is a free tool for observing qualitative features and making physical measurements (angle, length, area) of images. It can be used offline and downloaded from https://www.recolnat.org/en/annotate.
The software is based on the setting up observation projects that group together a batch of herbarium images to be studied, associating it with a descriptive model. A file of measurements can be exported in comma separated value (csv) format for further analysis (Fig. 2).

XPER3

Usually used in the context of systematics in which the items studied are taxa, XPER3 can also be used to distinguish architectural groups that are not phylogenetically related.
Developed by the Laboratoire d'Informatique et Systématique (LIS) of the Institut de Systématique, Evolution, Biodiversité in Paris, XPER3 is an online collaborative platform that allows the editing of descriptive data (https://www.xper3.fr/?language=en).
This tool allows the cross-referencing of items (in this case architectural groups) and descriptors (or characters). It allows the development of free access identification keys (it means without fixed sequence of identification steps). The latter can be used directly online. But it also offers to produce single-access keys, with or without using character weighting and dependencies between characters.

Links between XPER3 and Recolnat Annotate

The descriptive model used by Recolnat Annotate can be developed within the framework of XPER3, which provides for characters and character states. Thus the observations made by the Recolnat Annotate measurement tool can be integrated into the XPER3 platform. Specimens can then be compared, or several descriptions can be merged to express the description of a species (Fig. 3).

RESULTS

The joint use of XPER3 and Recolnat Annotate to manage both herbarium specimens and architectural patterns has proven to be relevant. Moreover, the measurements on the virtual specimens are fast and reliable.
N. Hallé (1977) had produced a dichotomous single-accesskey that allowed the identification and attribution of a pattern to a plant observed in the field or in a herbarium. The project to build a polytomous and interactive key with XPER3 required completing the observations to give a status for each character of each vegetative architectural model.
Recolnat Annotate was used to produce observations from herbarium network in France. The use of XPER3 has allowed us to redefine these models in the light of new data from the herbaria and to publish the interactive key available at dendrobium-nc.identificationkey.org.