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Published In: Species Plantarum 2: 1100. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/5/2009)


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1. Isoetes L. (quillwort)

Plants perennial, heterosporous. Stems fleshy corms, 2- or 3-lobed. Leaves quill-like, linear, hollow (with 4 chambers), the bases broadened and convex, bearing the sporangium in a shallow pit on the inner side and a thin scale, the ligule, above the sporangium. Sporangia thin-walled, partially covered along the margin by a flap of tissue, the velum. Megasporangia with 50–300 trilete megaspores, each 0.25–0.80 mm in diameter, trilete. Microsporangia with 150,000–1,000,000 monolete microspores, each 20–55 mm long, monolete. Gametophytes endosporic, retained within the megaspore walls. One hundred to 150 species.

Species of Isoetes are best distinguished by characters of the megaspores, leaf bases, and habitat. A hand lens is necessary to determine the texture of the megaspores, and microspores are visible only under higher magnification Thus the species can be difficult to identify. Most species undergo an annual cycle of leaf production in which the first leaves of the season are sterile, followed by leaves with megasporangia, then leaves with microsporangia, followed by late season leaves with abortive sporangia.


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1 Megaspores with a raised network of narrow ridges 2 Isoetes engelmannii A. Braun var. engelmannii
+ Megaspores smooth or with faint wrinkles or tubercles (2)
2 (1) Megaspores mostly 0.45–0.65 mm in diameter; outer surface of leaf bases white to tan or brown, not shiny 1 Isoetes butleri
+ Megaspores mostly 0.25–0.45 mm in diameter; outer surface of leaf bases usually black, sometimes brown to pale brown, shiny 3 Isoetes melanopoda
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