Fyto: Autoregressive Language-Model Inference Powered Solely by a Living Houseplant

Published plant- and soil-microbial-fuel-cell (PMFC/SMFC) electronics run duty-cycled sensing and a radio; none runs a neural network. We present Fyto, a sealed box in a potted golden pothos (Epipremnum aureum) that generates text with a llama2.c-class transformer on an Ambiq Apollo4 Plus microcontroller, with two hydraulically separated PMFC chambers as its only energy source and output leaving through a galvanically isolated UART. No Fyto hardware has yet been measured: energy figures are emulated or modelled, and the claim that a plant powers inference is a pre-registered hypothesis. Instruction-level emulation of verified Cortex-M4 kernels gives 3.1–3.5 cycles per int8 multiply–accumulate, about twice the usual assumption; the resulting model gives 18–55 µJ per token for a 1.1 M-parameter model (36–55 µJ at the emulated cycle counts; the low end assumes a hand-scheduled 1.75-cycle kernel). Pots delivering the tens-to-hundreds of microwatts reported in the literature still sustain 2×10⁴–5×10⁵ tokens per day (revised chain, Monte Carlo p10–p90). The binding constraints lie elsewhere: an always-on chain idles at 34–69 µW, the specified harvester's fractional-Voc tracking (70–90 %) captures at most 0.61 of the power of a cell whose maximum power point sits at 0.42 Voc; and retained SRAM costs more than the plant supplies. A revised chain with per-chamber constant-voltage harvesting, a decifarad store, power-gating and per-token MRAM commits idles at 1–2.5 µW and wakes in 99.7 % of draws. Running the real stories260K checkpoint, we measure 0.446 words per token and show that per-token commits resume bit-exactly in all 600 fault-injection runs (1,513 brownouts), against 187 of 600 runs (31 %) for a naive ordering. Because a gram of soil carbon could power this load for decades, we pre-register controls (unplanted, sterilised soil, darkness, plant removal, electrode swap, titanium-only, galvanic), an energy ledger, a coulombic-overdraft test and a ¹³CO₂ electron budget that would measure, for the first time in any plant fuel cell, the fraction of charge, and so of tokens, paid for by freshly fixed CO₂. Preprint v1. Code, data, figures and LaTeX sources are included in fyto-paper-v1-code-data.zip. Project: fytopure.online.